THE percussion figures that Mr. Holland has discovered both are interesting in themselves and seem to be a very handy means of marking off one crystal from another in thin lake ice. Their symmetry about a vertical axis is evidence that the optic axes of the crystals were vertical. The small amount of snow here this winter has afforded unusual opportunities for examining the ice on the Davos lake, and I have found crystals, not indeed equal to those on the Welsh lakes, but still very large. A striking feature in the ice, about a week after it was strong enough to bear skaters, was the presence of a number of hexagonal disks, of all sizes up to a quarter of an inch diameter, with their planes apparently horizontal. Some were regular hexagons, but generally the sides were unequal, though the angles were always 120°. I concluded that within a single crystal all the hexagons would be similarly oriented, and that an interface of two crystals could be distinguished by a sudden twist in the direction of the sides. Judged by this test some of the crystals were at least a foot broad, and in depth no doubt equal to the thickness of the ice, at that time about a foot. To verify this conclusion Mr. Kidd hacked out a piece with the axe, and we prepared a rough plate six inches long and three thick, which we examined in the polariscope. The rings and cross were easily seen, and the plate proved to be all one crystal with the optic axis vertical in situ.