that it was from the examination of the small pools he first came to the conclusion that glaciers scooped out basins in rock; that he was at first "too timid to include the larger lakes;" and that becoming convinced the larger lakes occupied true rock-basins, he included them in the category of lakes which had been formed by the agency of glacier, because glacier alone, in his opinion, is capable of excavating true rock-basins!
The smaller idea has been shown to be fallacious, and it might be said that the larger one, which is built upon it, necessarily falls through. This is scarcely the case. The former deals with square yards, and the latter with square miles. A glacier we know, as a matter of fact, polishes down a quartz-vein in the same way as it does a bed of soft limestone. A plane which is adapted for planing wood may cut through a nail in a plank whilst taking off a shaving. But the plane is unable to take a shaving off a solid mass of iron, and it might be said, with some plausibility, that a glacier might be equally impotent if it had to work over square miles of quartz instead of square feet. To form a just idea of the probability of a glacier producing a lake-basin in one place (in soft strata), when during the same, or a longer, period, it only slightly erodes the surface at another place (hard strata), we ought to find out the effects which are actually produced by glaciers when working over a series of strata of unequal hardness, where the strike of the beds coincides with the direction of the motion of the ice. The idea, indeed, has often occurred to me, that insignificant quartz-veins might resist the grinding of glacier if they were worked upon longitudinally. It is not, of course, an easy thing to find a vein of quartz which has been worked upon longitudinally for a considerable distance; and I have never observed a better example than that which is described in the following paragraph.
In 1867, upon the shores of a fiord, about nine miles to the east of the settlement of Claushavn in North Greenland, I had the good fortune to discover the finest examples of roches nivelées which I have seen anywhere. The great interior mer de glace was near at hand, and a branch of it closed the inlet with an unbroken wall of ice,
