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The Pamphlet Collection of Sir Robert Stout: Volume 22

2.Insufficiency of Icebergs or Coast-ice to account for the Phenomena

2.Insufficiency of Icebergs or Coast-ice to account for the Phenomena.

—Perhaps some may attribute the numerous striated surfaces, as well as the Boulder-clay, to the action of icebergs or coast-ice on a sinking area; but a little consideration will show that either of these causes is quite inadequate to explain the phenomena. We have shown that over the whole of Shetland the glaciating agent must have conformed to the inequalities of the surface, descending into page 808 the smallest hollows and overflowing the projecting knobs of rocks, indicating in an unmistakable manner that the agent must have pressed steadily and firmly over the whole area. Nay, more, the islands have been grooved and striated in one determinate direction, while rocky slopes have boon likewise abraded; and from the manner in which the stria; run obliquely up the hill-face, it is evident that the agent must have ascended the slopes, and ultimately overflowed the high grounds. Now it is hardly necessary to point out that neither coast-ice nor icebergs are capable of producing such results as these. It is impossible to conceive that icebergs or coast-ice could press steadily on a wide archipelago like Shetland, so as to plane down the inequalities on the surface; far less could they produce this uniform system of striation. "We may well ask, by what means could floating ice or coast-ice ascend a rock-slope several hundred feet high, leaving at the same time indelible impressions of the upward movement? Such an occurrence would be a physical impossibility.

Again, the phenomena of the Boulder-clay are quite at variance with the floating-ice theory; for if this deposit be due to the droppings of icebergs or coast-ice, then assuredly it would have been more or less stratified; whereas, from one end of Shetland to the other, the Boulder-clay, with but few exceptions, is quite amorphous. If it be really a marine deposit, how could it possibly partake of the characters of the rock-formation on which it rests, and how could the relative ingredients diminish in number in proportion to the distance from their parent source?

Further, the occurrence of blocks in the Boulder-clay on the western sea-board of Unst and the Mainland, which must have crossed the watershed to reach their present position, is still less explicable by this hypothesis. For if the high grounds of Unst or the Mainland were submerged so as to allow a free passage for icebergs in their westward career, where are the areas of gabbro, serpentine, or Old Red Sandstone which could have supplied the materials found in the Boulder-clay? Even if we suppose that ice rafts drifted off the eastern sea-board laden with such materials, we must suddenly invoke a special subsidence of several hundred feet at least, both in Unst and in the Dunrossness area, to enable them to cross the watershed. But this improbable supposition still leaves unexplained the relationship which exists between the relative distribution of the stones in the Boulder-clay on the west coast, and the relative areas occupied by the rock masses. For these reasons, therefore, and others Which it is not necessary to specify, it is impossible to reconcile the glacial phenomena of Shetland with the theory of icebergs or coast-ice.