Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/946

 Ireland, " Oscars " in Sweden) ; so that, unless this stumbling-block be removed, we must consider them due to fresh- water action — this action being still unknown. The mounds on the " Mound Prairie " in Washington territory 1, and also in Texas, are, I am convinced, very similar in their origin, though I doubt if the cause, or causes, engaged in forming them were in any way connected with the glacial period. My eminent friend Professor J. D. Whitney's denial 2 of the presence of the glacial drift on the North Pacific coast (whatever may be said of the region he is personally intimately acquainted with, as Director of the Geological Survey of California) is founded, as far as British Columbia, Washington Territory, and Vancouver Island (so far as I have examined these countries) are concerned, on the imperfect observation of his informant 3, the drift being everywhere well developed in these regions, as I have pointed out in another place 4.

4. Boulders. — Boulders scattered over the country are due to the period of the formation of the (non-fossiliferous) Boulder-clay when the country was sunk more than now, as will be afterwards noted in the inferences (§ β) ; but those lying in the lines of valleys are due to the depositing power of bergs, as these bergs still, as described, deposit them in the originals of these glens and valleys, the Arctic fjords; and hence the boulders keep the lines of the valleys. The boulders and travelled blocks on the top of the highest hills are due chiefly to the transporting power of the great moving " inland ice " of Britain at that period ; and the former are really a portion of the moraine profonde, which, however, the old rivers (derived from the melting of the glacier-cap) or the subsequent action of the weather have not swept, with the clay around them, into the valleys. These boulders, dragged over the rocks, would act as a file to the underlying strata they came into contact with ; so that we need not be surprised that both the rocks and boulders are deeply furrowed.

We must, however, draw a distinction between the different kinds of blocks scattered over the country. Those blocks, rounded, grooved, and worn as if by ice could (in my opinion) be only due to this moraine profonde, and are connected with the superincumbent inland ice. The boulders &c. carried off by bergs are not grooved or worn ; for they merely drop down on the upper surface of the ice and are carried out to sea, and there dropped. If they are afterwards grooved it must be by the action of ice passing over them and grazing them — an occurrence, I fancy, not very common. That these erratic blocks will get water-worn is only a natural con-

1 Gibbs, in ' Pacific Railroad Surveys,' vol. i. pp. 469 & 486 ; Cooper, in the ' Natural History of Washington Territory,' p. 18. These and other physico-geographical features of North-West America will be more fully described in the author's ' Horae Sylvanae ' now in course of publication.

2 Proceedings of the California Academy of Sciences, vol. iii. p. 277 (1866).

3 See also Dall, in ' Silliman's American Jour. of Sc.' Jan. 1868, and Proc. Boston Nat. Hist. Soc. vol. xii. pp. 145, 146.

4 Petermann's ' Geographische Mittheilungen,' 1869, p. 5 ; Trans. Geol. Soc. Edin. 1869, p. 19 ; and ' Silliman's Amer. Journ. of Sc.' Nov. 1870, pp. 318-324.