I. Introduction.

In the course of our annual leave of absence from official work, we visited Caithness in the autumn of 1880, for the purpose of continuing our investigations regarding the extension of the ice in the North Sea in the Glacial period. The results of our previous observations in Shetland and Orkney, which have appeared in the Quarterly Journal of the Geological Society^* point to the conclusion that during the climax of the Ice Age the Scandinavian and Scotch ice-sheets coalesced on the floor of the North Sea, and that a great portion of this ice-field moved in a north-west direction towards the Atlantic. We showed that a careful examination of the roches moutonntées, the striated surfaces, and more especially the dispersal of the stones in the boulder clay, compelled us to admit an ice movement from the North Sea to the Atlantic during the primary glaciation. We inferred that the Shetland group must have been overridden by the Scandinavian portion of the ice-field, as the striated surfaces clearly point in that direction; while the presence of Scotch rocks in the Orcadian boulder clay led us to the conclusion that these islands must have been overflowed by the Scotch ice-sheet. Further, we adduced evidence to prove the existence of local glaciers in Orkney and Shetland long after the great mer de glace had melted back from the old coast lines of these northern islands.

The glacial phenomena of Caithness have an important bearing on the general question of the extension of the ice in the North Sea, and although they have been described by many writers, we resolved to visit the county with the object of gathering evidence regarding the direction of the ice-flow and the probable physical conditions which prevailed during the accumulation of the superficial deposits. In the sequel page 4 we hope to show that in many respects there is a close resemblance between the glacial phenomena of Orkney and those of the Caithness plain. We obtained evidence which shows that the local ice, shed from the hilly ground along the county boundary, moved E., N.E., and N. till it debouched on the plain, where it was compelled to veer round to the north-west in harmony with the general movement in the low ground of the county.