Page:A Treatise on Geology, volume 1.djvu/311

 CHAP. VI. difficulty force their way. Over the intermediate area the ice-bergs would be constantly strewing masses of rock and detritus, particularly at their northern limit, where they would probably form mounds resembling terminal glacial moraines ! As the stranding of icebergs would happen on sandbanks and shoals, we might expect accumulations from this cause to be more prevalent on hill tops, and along the sides of broad vales, than in the depths of valleys; and such is well known to be the fact in many examples of erratic blocks.

Thus, in describing the vast extent of detrital deposits on the broad surface of European Russia, in fact, from the German Ocean on the west to the White Sea on the east, Murchison expressly marks the discontinuity of the erratic masses, and their greater frequency on plateaux, and especially on the southern sides of these plateaux. Accumulations of like nature form hills (escars in Ireland, osars in Scandinavia, barfs in England), in which often some peculiar disarrangements may be remarked in the accumulated detritus, not unlike that in true 'moraine.'

A difficulty which occurs in receiving glaciers on land and icebergs at sea as a full explanation of the phenomenon of transported blocks is this:—Two cases have been pointed out by the author of this treatise, where, beyond all doubt, portions of remarkable rocks have been lifted by the transporting force to much higher levels on neighbouring hills, and under conditions which leave no room for supposition that the difference of land has been occasioned by unequal movement of ground since the dispersion of the blocks. In one case (Craven) large masses of lower palaeozoic slaty rocks are lifted up in great numbers on to the limestone which lies level on this very slate. In another (Stainmoor), a red conglomerate, of very peculiar character and local