Science Lectures for the People., Second Series.
The Natural History Of Paving StonesBy Professor Williamson, F.R.S.,
Manchester: John Heywood, 141 and 143, Deansgate. London: F. Pitman, Paternoster Row
Price One Penny each.
The First Lecture of the Second Series, by Professor Huxley, LL.D., F.R.S., on "Coral and Coral Reefs."
The Second Lecture of the Second Series, by Professor Roscoe, F.R.S., on "Spectrum Analysis."
The Third Lecture of the Second Series, by W: Huggins, LL.D., D.C.L., F.R.S., on "Spectrum Analysis in its Application to the Heavenly Bodies."
The Fourth Lecture of the Second Series, by W. Boyd Dawkins, Esq., M.A., F.R.S., F.G.S., on "Coal." With Illustrations.
The Fifth Lecture of the Second Series, by Professor Ward, on "Charles Dickens."
The First Series of Science Lectures for the People:—A Course delivered in the Session of 1866-7, comprising the following:—
Four Lectures on "Elementary Physiology." By Dr. J. E.Morgan.
Price One Penny. A few of Lectures 2, 3, on "Elementary Chemistry." By Professor Roscoe, F.R.S.
Price One Penny.
A few of Lectures 5, 6, 7, on "Elementary Zoology." By Dr. T. Alcock.
Price One Penny.
One Lecture on "Coal: its Importance in Manufactures and Trade." By Professor W. S. Jevotis, M.A.
Immediate application is necessary, as but few copies remain.
In the Press, a complete New Edition of the above, uniform with the present series, and will be published shortly.
The Natural History of Paying Stones.
Dr. Roscoe, who presided, said:—I have great pleasure in re-opening the series of "Science Lectures for the People;" and I have the more pleasure because my friend Professor Williamson has consented to deliver the first lecture. I am afraid that the title he has chosen has given some people the idea that it would be a dry lecture. I know, however, that all those who are present will not only not regret that they have heard the lecturer, but will feel sorry that they did not bring their friends with them; for, like the giant in the story, Professor Williamson will extract for us interest and benefit even from paving stones.
Professor Williamson said:—Ladies and Gentlemen,—When, some century and a half ago, the first excavations were made into the lava masses that covered the ancient city of Pompeii, it was discovered that the streets of the city had been paved with blocks of lava from the adjoining mountain Vesuvius. You have probably all heard of Macaulay's apochryphal New Zealander, who, in some future age, when England has passed its zenith, and is once more become a desolate wilderness, is to sit upon one of the broken arches of London Bridge to sketch the ruins of St. Paul's. And if that topographer of the future, when he accomplishes the task that the brilliant essayist assigned to him, visits the city which tradition indicates as having been the ancient seat of manufactures in this part of the country—I mean the city of Manchester—he, if he has assistants with him and should make similar explorations in the streets of this city, will have to record the same fact that has been recorded page 4 of ancient Pompeii. Unexpected as the fact may be even to you, he will have to announce that the streets of the city were chiefly paved with lava from an adjoining mountain.
Now before I demonstrate this apparently paradoxical statement, I must call your attention to the fact, which probably most of you know already, that there are two very different kinds of rocks found in the interior of the globe. There are, first, those that have been produced by volcanic fire—lavas—of an endless variety of sorts. There are, secondly, what are called the stratified rocks, that have been produced by the action of water. If you see a muddy pool depositing layer after layer of mud, and if when this mud subsequently becomes dried up, you proceed to examine the muddy deposit, you will find that it is arranged in layers. Now this deposit is on a small scale an epitome or picture of what is taking place on a gigantic scale in lakes and seas throughout the entire world. Every part of the world has been under water at one time or another; and the deposits that have been produced during countless ages have given us what we call the "stratified rocks." But you will probably like to have a proof of everything that is said from this platform. You may ask—How do you know that these deposits have been formed by water ?
I wont dwell upon the subject; I will merely say that where we find oysters and mussels, and cockles, and crabs, and lobsters, we are pretty safe in affirming that the deposits which enclose the remains of those marine creatures must have been formed somewhere in the neighbourhood of the place where these marine creatures lived. And so the marine remains of fossils that we find in these rocks clearly testify to the fact that the rocks in question were formed by watery agency and under water. But you say, in the second place, even supposing we accept that proof as satisfactory, what evidence have you to give us that the other rocks were formed by fire? As this will be the special subject of a portion of my lecture to-night, we will take a little more trouble to demonstrate this fact to you, and make it plain.
The first photograph that I will show you is one from a drawing in a work recently published by Professor Silvestri, a work in which he gives an account of the changes that have taken place during the last few years through the eruptions of Mount Etna. Here you have a view of the summit of Etna; the central peak is here. I need scarcely tell you that you are looking down upon it as if from one of the balloon posts, about which we have heard so much latterly. All these round knobs that stand out so numerously and so prominently are so many craters that from time to time have burst page 5 through that mountain. There are hundreds of these craters, and a large number of them constitute even decent-sized volcanic mountains, scattered round the slopes of Mount Etna. Then these large black spaces, to which I would particularly call your attention, are areas where the lava has burst through some of these craters. Of course it has filled up the crater through which it flowed; but, in addition to filling the crater, it has overflowed its summit, and spread itself out in broad table-like areas over the sides of the mountain, and over the surrounding plains. Now, we have here an illustration of the kind of thing that these volcanic mountains exhibit. You may be somewhat surprised if I tell you that those slopes of Mount Etna are scarcely more pierced by craters and encompassed by deposits of lava than Wales is, in our own immediate neighbourhood. There has been a time when Wales was almost as much disturbed by volcanic fires as Sicily is now. If you were to take a geological map of Wales, you would see that it is studded all over and in every direction with little red spots. Those little red patches are colours employed by geologists to indicate masses of ancient lava. Wales abounds in these masses. We find them on every hand, and it is to some of them, in the first place, that I shall have to call your attention to-night. I will show you a section of a part of Wales where we have volcanic rocks, and stratified or aqueous rocks, side by side, or rather, the one within the other. A section, you will understand, is that which you would have if I were to cut a Dutch cheese in two, and show you the cut side of it. If the Dutch cheese had happened to have been made of layers, piled upon one another like a pile of sandwiches, you would then have the edges of the layers revealed to view. But here, instead of sandwiches, we have a series of layers of stratified rocks; and, in the middle of them we have a great mass of volcanic lava. This is a mass of ancient lava from one of the Welsh mountains, with an unpronounceable name. I dare not venture to utter it. I should only fail; because, as you know, it is not easy to say which are consonants and which are vowels in the Welsh language, unless one is trained to it, which I was not. These are slate rocks. You will observe they are arranged in sloping layers, but these layers were originally horizontal. The reason why they slope upwards is that the volcanic fires which accompanied the outburst of this lava mass has driven up these stratified rocks, tearing them asunder, whilst the lava has forced its way through. We have several reasons for affirming that this lava was once fluid. You will observe that the page 6 lava has not only broken through these stratified rocks, but flowed upwards and downwards in all directions, filling cracks and crevices, which would not have happened had this lava not been fluid. Before I give you another section illustrating to you this action, let me show you a section of Snowdon itself, cut in two. You shall also see the summit of Snowdon, which a kind friend who is in the room has brought to us. Then we have here a section of Snowdon. Here you have the extreme summit of Snowdon—the point to which many of you probably have been. You will observe that there are several series of rocks following each other. Now what, in the first place, are these purple-coloured layers at the base?(The colours are merely conventional, for the purposes of the diagram.) They are beds of slate rocks. These yellow-tinged parts above them represent enormous masses of lava. Now, this mass of lava was once continuous over many miles of district. The reason why it is now isolated is this: after spreading over many miles of district, it has been subjected to the action of currents of water when the whole was under the sea. These water currents have scooped out deep valleys, and swept away an incalculable number of square miles of solid materials. Parts of Wales that were once thousands of feet higher than they are at the present day, have been completely cleared away by this watery action—by what is technically called "denudation." This accounts for the interrupted character of these masses of deposit. The summit of the mountain is a mass of volcanic product, not lava, but ashes. It would appear as if the volcanic outbreak which had covered this part of the country with this peculiar kind of volcanic rock, had been followed by some outburst such as you meet with in volcanoes of the present day, in which an enormous quantity of volcanic ash has been deposited; and some of what escaped removal by denudation now constitutes the extreme peak of Snowdon. The next picture will show the peak of Snowdon as it now is. The difference between the present and the past is very considerable. I do not mean to say that the cairn is a volcanic peak; it is not; but the material upon which the wonderful cairn is erected is volcanic; it is made up entirely of volcanic ash. So that we have in Snowdon three distinct masses of material—the volcanic ash at the top; a mass of lava in the middle; and the water-derived slate rocks at the base. In the diagram I showed you just now, you saw a broad red band crossing the picture obliquely. Now this band is another kind of volcanic rock, and of more modern date than the page 7 others. You ask, "How do we know that?" Well, I think we may safely venture to say that that which goes through another thing, has come there subsequent to the time when that which it penetrates first existed. These rocks, you perceive, have been already deposited when some huge volcanic crack has been formed in them, and volcanic material has come up and filled that crack. Here we have evidence of successive outbreaks of volcanic action. Now I will show you the proof that this volcanic action was accompanied by heat. I think I have said enough to show that this material must have been fluid. The reasons why we conclude that that fluid must have been in a heated state like lava, are these. In the first place, wherever the lava has come in contact with any other kind of rock, it has entirely altered the character of that rock. If it has come in contact with coal, it has burned that coal into cinders; if it has come into contact with limestone, it has burned that limestone into marble; and if it has come into contact with slates, it has altogether altered the character of those slates, and given them a different appearance. I will show you an instance proving this point. The picture that I am now going to exhibit to you is a section of another part of Wales, derived, as most of these sections are, from the very able report on the Geology of Wales by Professor Ramsay, and which was published in the Memoirs of the Geological Survey of England.
Here we have a series of slate rocks with a dyke of lava running through them. Here is a fragment of slate torn off from these rocks and embedded in the lava. You will observe that the appearance of the slate immediately above and below the lava is altogether altered. The difference is this—one portion of the slate cleaves easily into roofing slates; but the layer in immediate contact with the lava has been so altered by that contact that it refuses to be so cloven. Now you have here a clear proof that the contact of the lava with the stratified or aqueous rocks has made an entire change in the structure of those rocks; and we know from examination that all these changes, wherever we find them, are precisely the phenomena that would result if the same rocks were exposed to the action of heat.
The next point that I will speak of is the more special subject of the lecture to-night. I am going to tell you about paving stones. As Professor Roscoe has intimated to you, it is a somewhat unpromising subject; and I confess I was rather disposed to approach it with a little fear and trembling. In Manchester, as I learn from our friend Mr. Stott, who has charge of this department, we use different kinds of stones for paving. I have here page 8 three stones of one kind, and several stones of another kind. Before going into details, I must remind you that we have in Manchester an ancient civilisation and a modern civilisation. If you go along the back streets of Ancoats and other parts of the town, it will be desirable, especially if the day be wet, to take care to have thick shoes, because walking in thin shoes on the rounded boulder stones with which those older streets are paved is somewhat uncomfortable work. But our civilisation has made Our more modern streets very different. You know that they are paved with those square stones which I think are technically call "sets," stones which make a magnificient paving. The only complaint we hear about them is when our authorities do not supply the streets with quite sufficient water, and then the gentry who ride their horses or drive their carriages are a little disposed quietly to complain. But this is only one very insignificant feature of these stones. It is true they are apt to become a little slippery in dry weather; but on the other hand, they are exceedingly durable, and being durable they are eminently fitted for the purpose of the tax-payer, whatever they may be for the equestrian. I learn from Mr. Stott that we obtain these "sets" from three localities. Here is one stone that is obtained from Penmaenmawr. Here is another stone that has been obtained from the Clee Hills in Shropshire; and here is a third stone that is obtained from a part of Carnarvonshire, from the neighbourhood of a place they call Glynnog. What are the rocks at these three localities?The Penmaenmawr and the Clee Hill stones are very similar in their essential qualities; they are lavas, closely allied to the forms we commonly call basalts and greenstones. I wont enter into the minute distinctions of these stones. I am not about to bewilder you by the wonderful chemical formula that my friend behind me (Dr. Roscoe) could favour you with, in describing the chemical composition of these stones; that would be out of my reach and line. Neither will I trouble you much with minute distinctions between one kind of basalt and another. There is an endless series of these distinctions that would perplex any philosopher to define, and it would perplex him still more to identify all the varieties when he saw them. All I have to do with them to-night is to say that there are many kinds of lava, whether we choose to call them basalts or greenstones, or felspars or porphyries or by any other of those mineralogical names which are employed to distinguish them. But we can draw a broad distinction between basalts, an ancient kind of lava, and granites, which are also an ancient kind of lava, but a very different one. Let us see what this Penmaenmawr stone is. page 9 It is a lava very similar in its essential composition to the lavas of modern times. Let us see what sort of appearance these rocks present as seen in a photograph. I have here two photographs of Penmaenmawr, a place that probably many of you have visited. One is a view from the north side, and the other a similar view from the south side. Here you have Penmaenmawr as it appears from the south side.
You observe that we have here a sloping plain. Now this plain consists chiefly of stratified rocks of various kinds. But you notice that Penmaenmawr is a huge rocky mass that rises up out of the plains—a huge boss. Now, let us see the other side of Penmaenmawr. When viewed from the opposite side, it presents precisely the same features as before. Here you have Penmaenmawr as seen from the village itself. You observe that from this side, you again have a large plain, made up of stratified rocks, with this immense boss of lava that has been forced through from below. The section I am about to show you is from the very heart of a mountain called Mynyddmaior. It consists of substantially the same rocks as Penmaenmawr. Now notice the stratified rocks. They have been thrown into almost vertical positions by the outburst of this lava. When the denuding currents have swept over that country—as I have told you they have done, again and again, through countless ages—they have removed all those portions of the rocks that were softer than others; they have yielded to the action of the water, whilst the harder rocks have resisted it. Now this lava being harder than the stratified rocks, has resisted that action; and, therefore, it stands out like a huge boss from the surrounding plain, precisely in the same way that we have seen that Penmaenmawr stands out from the plain surrounding it. It is simply because this crystaline lava is very much harder than the rocks around it that it stands in this fashion; it has resisted the denuding action; the other rocks have yielded to that action. Here then we have a clear illustration of the nature of the rock of which Penmaenmawr consists, and which we are using to a very considerable extent for the purpose of paving the streets of Manchester. We will now leave Penmaenmawr.
Let us next see what we have got in the Brown Clee Hills. Mr. Stott informs me that the Clee Hills stone will serve our purpose better than the Penmaenmawr stone. He believes it to be a harder stone. But when we examine the conditions under which it was formed, we discover that it is substantially the same thing we have had before. Here you have a section of the Clee Hills. At the base we have a limestone, similar to that which page 10 you have in the hilly districts of Derbyshire. Then we have here the millstone grit—that coarse grit—stone found in the hills behind Oldham and Rochdale. Then, at the upper part, we have a coal field, furnished with seams of coal like those that we find in this neighbourhood. But this red band running up through the centre of the section, and overflowing right and left, is really lava, very similar to what we have seen at Penmaenmawr, a crystaline basalt, which is spread out over a very considerable area, forming an extensive moorland district; and it is from this district that this Clee Hill basalt is now being brought to Manchester. Thus we see that the phenomena attending the formation of this Clee Hill basalt are precisely the same in all essential features as those that have attended the formation of the basalts in Wales.
We have now to look at the third stone. You are all more or less familiar with the name of granite. Granite has unquestionably been an ancient lava; but it has been rather different from modern lavas in a variety of secondary circumstances. We see very clearly, first from its composition, and second from its microscopic structure, that it has not been formed under the same conditions as the ancient lavas with which we are familiar. The probability is that it has been formed under greater pressure. Whether that pressure has taken place deep in the interior of the earth, or whether it has taken place, as some suppose, under a deep ocean, we have no means of knowing. But there are many minor and secondary features .about it which indicate that the conditions which make granite different from other stones, have resulted from an enormous pressure. But then we have two kinds of granite. Common granite is made up of three minerals, known by the respective names of quartz, mica, and felspar. But the particular variety which I hold in my hand, is that known by the name of syenite; and it differs from other granite inasmuch as the mica of ordinary granite is replaced by the crystals called hornblende. This is not a matter of any very great consequence to us, except for this reason, that the hornblende being somewhat harder than mica, we may fairly expect that the syenite may give us a harder paving stone than the ordinary granite. We will see what this syenite is like when at home. Here is a section which exhibits to us the locality from which this syenite is obtained. In it we again observe that we have the stratified rocks thrown upon end. The fact is, these stratified rocks, in Wales, as elsewhere, have been twisted and twined about almost as easily as you could twist and twine about page 11 layers of cloth or brown paper. The forces with which nature has altered the conditions of these strata, have been so gigantic that any resistance these rocks could afford has amounted to very little indeed. This syenite, you observe, presents itself to us under precisely similar conditions to those we have seen in the case of basalt. It comes up from below, filling a huge crack; and if we examine the sides of the crack we shall discover that the heat of the fluid mass of syenite has altered the rocks, just as the basalts and other lavas altered the stratified rocks.
We will now leave these "sets" and examine an altogether different branch of our subject. We must turn to the ancient Manchester paving, and this brings us to the boulder stones. We have to take into consideration two or three circumstances in connection with these boulder stones. I am informed by Mr. Stott, tl .at in the olden time, when we were in the habit of importing boulder stones for all the streets of Manchester, they were chiefly brought from the sea coast of Cumberland. If you go to the sea coast, either of Cumberland, or of any other land, you will find that it is frequently made up of rounded stones, anything but agreeable to walk upon; almost worse, if possible, than the rounded stones with which your older streets are paved. You might be disposed to imagine that all these rounded boulder stones had tumbled down from the cliffs above, and simply been rounded by the action of the water, by the waves beating upon them year after year and century after century. And in the case of many of these boulders you would undoubtedly be right in so surmising. I don't know much about the Cumberland coast, but I could take you to the Yorkshire coast, about which I do know something, and could show you there precisely similar phenomena to those which appear on the Cumberland coast; and we have every reason to suppose that the essential conditions are pretty much the same in the two localities. When we visit these coasts, whilst we discover a large number of rounded stones derived from rocks forming the adjacent cliffs, we also discover mixed up with them a very large number of stones that are not to be found in situ, as we call it, that is in their natural position, within miles from us. Here, then, we clearly have to seek out some agent that has assisted the sea. There has evidently been some other power at work that has brought boulder stones to that Cumberland coast that were not there originally, and that were not derived from the strata of the adjoining cliffs. We find there granites and lavas, and an endless variety of other rocks that were not originally page 12 derived from the Cumberland hills at all; they have been imported into that district and subsequently re-imported from that district to Manchester. Now whence have these other stones come? It will simplify the matter, as the Irish song says "altogether entirely," if we call your attention to a Manchester brickfield. You may ask, what on earth can a Manchester brickfield have to do with Cumberland boulders and the paving of Manchester streets? More than you would imagine at first sight. If I take a walk with you to a Manchester brickfield, we shall discover that we are most interested in precisely that part of the field that will be the greatest abomination to the brickmaker. The brickmaker likes the nice, smooth, soft clay, without any stones in it, which to the geologist is about as stupid a part of the field as he could have. The geologist, on the other hand, likes to find a place that is full of gravel and sand, and huge boulder stones of every shape, and sort, and size—the very abomination of the brickmaker. I have here certain boulder stones that were taken from a Manchester brickfield. What have I in my hand? A block of granite, which I carried painfully and laboriously one day from a brickfield in the neighbourhood of Ladybarn. It is a mass of granite, rounded just like the rocks on the Cumberland coast. That granite has been transported from a considerable distance, because we have no granites nearer than Cumberland. The nearest granite we have to this locality is that of Shap Fell, in Cumberland. The granite from Shap Fell is a very remarkable granite, from the large crystals of flesh colour which distinguish it. I have here, from this same brick-yard, a piece of Shap Fell granite. Why, I could swear to this piece of granite all the world over, as a man would swear to the face of his own wife wherever he met with her. The features of it are so remarkable that you could not mistake it, if you knew what Shap Fell granite was. Now this Shap Fell granite, rounded and water-worn, has been brought to a Manchester brick-yard. How has it got there? I have here another boulder. There is nothing particular about the appearance of this boulder, except that it is a piece of limestone that never "grow'd"—if I may apply Topsy's word—in the neighbourhood of Manchester. It, like these other stones, has been brought to Manchester from a distance. But it tells me another story. It has another tale to record. I see that this surface is grooved, as if covered with the marks of a file. I turn it round to the other side, and I see that it is filed and grooved in like manner; but these grooves are not parallel with the former grooves. Here is a second flat face. It is very evident that in some way both these faces have had a good scrubbing, that has involved page 13 something more than a mere washing of the face. I dare say we have some keen reminisences of the sort of scrubbing we used to get from the nurse's hands with rough coarse towels; but that is nothing compared with the scrubbing these stones must have had. There has been an action which has flattened that surface and grooved it at the same time. We want some agency that will do all these things together. You will remember that when my friend Professor Huxley lectured here at the beginning of this series of lectures, he pointed out to you in a very clear and prominent manner, how absolutely necessary it was that any theory that was propounded to explain a multitude of phenomena should "go upon all fours;" that is, it must be equal to the explanation of all the several isolated and detached facts that the theory is intended to explain. Now we want a theory that will explain all these things. We want a theory that will mix together rocks of all kinds, that will mix them up with clays and with sands, and with an endlessly varied set of materials. We want a theory that will make some of these rocks round and grooved and streaked. We want a theory that will explain why some rocks that are transported are as angular and as sharp as this specimen. In order to give you such a theory, I shall have to carry you half way across Europe. I will begin by taking you to Switzerland, and if you have as pleasant a voyage thither to-night as I had some months ago, I shall envy you the repetition of my enjoyment. Here is a photograph I took in one of the loveliest scenes in all Switzerland. Here you have the Mer de Glace, that great stream of ice which has been celebrated in almost all ages as one of the loveliest spots in Switzerland. The Mer de Glace belongs to that range of mountains of which the peak of Mont Blanc is the centre, and it is only a few miles away from that great mountain. This is a glacier. What do we mean by that? Those mountains which you see on all sides of the glacier are within the limits of perpetual snow; summer and winter, wherever there is a ledge upon which the snow can rest, it remains unmelted. This accumulation of the snow would in time entirely hide and bury the mountains, unless nature had provided some way for getting rid of the surplus. She has provided such a way. The pressure of the snowy mass on the upper parts, forces the lower snow down into the valleys. Then that snow, partly under the influence of the intense cold, and partly under the influence of the pressure to which the particles are subjected, becomes re-frozen, becomes consolidated, not into snow, but into a mass of solid ice; and by a wonderful series of changes, which my time will not allow me to explain, this icy mass page 14 flows down the valleys of these alpine mountains, fitting itself to the various curves, to the widenings and narrowings of these valleys, almost as if it were a fluid. Indeed, so wonderful has been this peculiar power of the ice to adapt itself to the shape of the valleys, that the late Professor James Forbes, of Edinburgh, arrived at the conclusion that ice, hard as it appears to be when you are skating over it, must have possessed a certain property of viscosity, a certain kind of fluidity, which enabled it to adapt itself to the various contours of the valley. Professor Tyndal, however, has given us a better explanation. He shows us that this downward steady movement is really accompanied by a crushing process, instantaneously followed in each atom by what he calls regelation, which means in plain English, freezing over again. The point we have to deal with is not this re-gelation. We may take the movement of the glacier as an accepted fact. These glaciers move from the higher valleys into the lower ones at a very slow pace, but one which is capable of being measured. But what takes place as they do so? These magnificent mountain peaks, composed in this instance chiefly of granite, are being continually disintegrated by the cold of winter, by the rain, storms, and various atmospheric agencies that affect the surface of the globe. Huge fragments come tumbling down from above, and of course these fragments fall from the ice. You will see running along here a band of rubbish that has fallen from above. You will see along here another band of rubbish that has fallen from above on the opposite side. The next photograph is one I took of the same spot, in the immediate neighbourhood of what is called the moraine, or, in other words, this band of rubbish. Here you have the mountain slopes that we descended. We crossed over these huge rocks. Here you see the ice-slope which we had to climb in order to get upon the glacier. You see here what kind of materials the moraine consists of. The whole of this mass of rubbish is resting, not upon the ground, but upon the ice, so that, as the ice moves, it carries all these rocks along with it, just as easily as you would carry your hat upon your head, and if it is one of the chimney-pot hats, I venture to say an enormous deal more easily ! This is what is called a lateral moraine, one running down each side of the glacier. There are other moraines. The next photograph that I will show you is from another glacier in the Chamouny valley—another of the Mont Blanc glaciers—but it shows a different part of the glacier. This is a very instructive picture to those who have not visited the real scene. Here is the lowermost part of the ice; here is the page 15 cavern from which the water issues—there is always a torrent of water rushing down—and here we have what is called the terminal moraine. You will understand that when these masses of ice come down from the cold valleysabove into the warm valleys below, the ice necessarily melts. Were it otherwise, those splendid scenes would become simply one sheet of polar ice. It melts, but the stones that it carries wont melt; consequently they have to stay there. As the ice melts, these stones drop down; and here you might almost imagine that you see them in the very act of dropping. These are stones that must have fallen almost the very day that I was there. Here is a glacier covered with ice; here are all the stones that form the moraine; here is the melting ice breaking off in blocks; and, as the ice breaks off and melts, the stones that break off with it tumble down as you see here. Now, you observe that in this way we have brought down to the lower valleys enormous quantities of material that lately had their home on the peaks of the mountains and in the valleys above. In this way we see that the glaciers not only receive from the mountains on each side immense masses of rock, but that they carry these masses of rock along with them down to the lower valleys. There is no doubt whatever that a very large quantity of material that we now find spread over the surface of the globe has been conveyed in this way.
But this alone would not account for the phenomena of our Manchester brickfields. We want something more. We have evidence clear as the sun at noonday, that the material of which our Manchester brick fields, and the brick-clays over a great part of the world are similarly composed, have been brought thither by water. They have been deposited under water. We frequently find sea shells in them. We have the clearest evidence, I repeat, that these remains have been accumulated under the sea. Unless we can bring our glaciers in some way into contact with the ocean, our theory will not fulfil Professor Huxley's requisition—it wont "go upon all fours." Let us see if we can find proof of that contact.
We will now transfer ourselves from Switzerland to Smith's Sound, in the Polar regions. Here is a drawing I have copied from one of Dr. Kane's sketches. Here you have what is intended for the sea. If you saw it in daylight, it would be a proper sea green. Here you have the rocks and lofty cliffs that surround the part of the country in which the phenomena I am about to explain exist. In the extreme winter these masses of ice extend right across the Sound, from side to side. As the summer approaches, the central ice breaks up speedily, and floats away; but long belts of ice page 16 hold their ground around the coast for a considerable part of the year, and sometimes they fail to break away from one season to another. Now these blocks, or masses of ice, technically called "ice belts"—because they belt round the coast—receive masses of rock in precisely the same way as the glaciers did in Switzerland. Thus we see that these blocks of ice would carry away with them blocks of stone, if any circumstances occurred to detach the ice from the land. The detachments take place perpetually, and they carry away with them these blocks floating upon their surface. They are huge icerafts, which sail southwards, impelled by Arctic currents. But this is not all. We have some glaciers in these polar regions, of precisely the same nature as those of Switzerland; but, instead of the polar glaciers being comparatively diminutive—a quarter, or half a mile across—the great Humboldt glacier is 50 miles across, from one side to the other; and yet that Humboldt glacier, which comes right down into the sea, is bringing stones along with it in precisely the same way as the other glaciers. Now, with such prodigious masses of stone-covered ice as this existing in the northern seas, you will not wonder that from time to time icebergs of the most gigantic size are met with, floating out of those northern bays and straits. Remember that what are called icebergs are merely either fragments of this belt of ice of these Arctic glaciers broken away, or portions of that huge mass of ice which in winter covers the whole of those regions—when you see that these ice formations exist on so gigantic a scale, you will not wonder that icebergs are met with in these seas, sometimes a mile in extent If you realise that, when you have an iceberg of this size, it floats with its summits two hundred or three hundred feet above the sea, and that it sinks below the water, some six or eight times its elevation, I think you will readily understand how that floating raft would be able to carry a very considerable slice of Penmaenmawr upon its surface ! I have here a picture of one of these floating rafts copied from Dr. Kane's book. I have represented it as well as I could. Here you have the ice, which has upon its surface huge blocks of solid rock. This was sketched by Dr. Kane as he saw it floating away into the southern regions. It is an exaggerated example; we do not usually see the rocks so huge in proportion to the size of the raft, but it will give you an idea of the kind of transporting power that these ice rafts have.
Now let us see how all this applies to English scenery. I have told you that the glacier moves steadily down the valley. You saw from the diagram that the glacier is cut up by page 17 deep fissures, called crevasses, that go down frequently to its very bottom. The stones that appear upon the surface of the glacier fall into these crevasses, and at the bottom they become entangled in considerable numbers in the solid ice. Many of them are angular. But you will also understand that if that vast mass of ice, filled with stones, is moving steadily downward over the rocks of which that valley consists, those stones will act like the teeth of a huge rasp; that they will plough, just in proportion to their size and sharpness and hardness, deep grooves in the rocks along which the ice is travelling. The stones themselves, being imbedded firmly in the ice, will scratch and scour over the rocks over which they move; and this is precisely what we find that they do. Sometimes the ice retreats, leaving behind the smooth and polished rocks, over which it formerly travelled; the changes of the seasons frequently lead to its doing so; the glaciers not unfrequently recede up the valleys in hot seasons and come down again in cold ones. When the ice recedes we see that the rocks are scored and grooved and polished in the way we should expect them to be. But if they receive this rough sort of treatment, what might we expect to be the result upon the teeth of the rasp? Workmen know perfectly well that when they use their files upon hard metal the angles get worn off. It has been so here. We could readily understand that if this stone was embedded in the ice, and formed one the teeth of bur great Arctic rasp, that its surface might well be flattened and grooved with longitudinal grooves. Here, then, we have an agent capable of producing grooves. Then, if these icebergs float upon the ocean, carrying rocks with them, they will travel southwards, carried by currents, and, as they come into warmer regions, they will share the fate of the Alpine glacier. Floating upon the sea does not save them; they melt little by little, and as they melt the rubbish that they are supporting falls to the ground. The fact is, we have here a grand Arctic Limited Liability Carriage Company! and it is one in which the liabilities, in a financial sense, are at a minimum and exceedingly small, whilst the transporting power is at its maximum, or exceedingly great. If we were shareholders in a limited liability company, these would be just the results that we should like to attain to if we could. Inasmuch as the floating rafts cost nothing, it is of no consequence to the company that they melt, and that whatever they carry goes to the sea bottom. If they were bringing our trunks from the Arctic regions, we should find out the difference between them and a good old wooden ship. But they melt, and whatever they sustain, trunks or stones, goes to page 18 the bottom. The result is that large portions of the sea bed are being strewed over with blocks of stones—angular blocks, rounded blocks, sand, rubbish: every conceivable kind of produce that those northern mountains furnish is being gradually brought southward, and scattered over the bed of the Atlantic at the present day. And precisely similar phenomena were taking place during one of the latest of the geological periods when nearly the whole of our island was under the sea. There was a time, comparatively recent, geologically speaking, when our island was under the sea, but when the mountains of Wales and Scotland stood out like islets from the Arctic ocean. The great valleys of Snowdon were filled with these glaciers. If you go up the Pass of Llanberis, you will see on every hand the indications of the fact in the rounded rocks, and in their scored surfaces, that abound on each side of the road. A little above the village you see them beautifully exhibited; and in the same way, throughout in the district of which Snowdon is the centre, you have these indications of glacial action so numerous and so clear, that, not a shadow of a doubt remains that the Snowdonian valleys, as well as the valleys of Cumberland and Scotland were, at the time of which I am speaking, filled with ice glaciers. Now all these glaciers—along with others coming from hundreds not to say thousands of miles away, as well as from mountains in the immediate neighbourhood brought their produce to the same bed of the ocean, and as it was all tumbled down into one common mass, you find materials in the shape of mud and sand as well as coarser materials, including both rounded and angular blocks, accumulated in the same sea bed. Now I think you will see that I have brought before you an explanation that fully accounts for the miscellaneous kind of admixtures that you find amongst the sand, and clay, and gravel beds whether of a Manchester brickfield or of the coasts of Cumberland and Yorkshire.
Ladies and gentlemen, I have now finished my task. I have endeavoured, I trust not altogether unsuccessfully, to show, you that in the natural world there are no objects, however common and familiar, that cannot reveal an interesting story, if we are but intelligent enough to question nature in a right manner. Many of you are occupied with manufacturing pursuits, and, from time to time, your workshops receive the visits of strangers, who look with intelligent interest upon the processes in which you are engaged, and upon the final products of your labours. I invite you, in like manner, to visit nature's workshop. She, too, is a fellow-labourer with yourselves; only, unlike you, she needs no page 19 rest, but works on, with untiring energy, dayand night, summer and winter. She usually toils so noiselessly that few men know the vastness of the forces at her command. When we float idly upon a summer sea, or recline in some sheltered nook, watching the tranquil glories of a July sunset, we reck little of the fearful energies that underlie the present calm. It is only when Nature rouses herself, like some angry lion, that men recognise her terrific powers. It is when the reeling earth is shaken by the earthquake, and cities crumble into dust; when the volcano belches forth its showers of ashes and streams of liquid fire, hiding the prostrated ruins from the eyes of men; when the flashing lightnings and the grand roll of the thunder inspire the stoutest hearts with wonder not unmixed with awe; when the stormy ocean and the flooded river inundate the land, tossing man's proudest works, like playthings, from their surface, and hurling them to destruction, then it is that we learn something of Nature's power. Yet these forces, at times so terrible, are ever working out their Divine Creator's will and ministering to human wants. Study them and they will interest you; examine their products and they will repay you. You will then recognise the truth of the words which our greatest dramatist puts into the mouth of his banished duke, when he declares that there are
Tongues in trees, books in the running brooks,
Sermons in stones, and good in everything.
On the motion of Mr. John Plant, F.G.S., thanks were given .to Professor Williamson for his interesting lecture.
John Heywood, Printer, Excelsior Works, Hulme Hall Road, Manchester.