The usual mode of accounting for the bone-breccias so eommonly found in caverns open to the day can scarcely be considered by any body as quite satisfactory. It seems usually taken for granted that that mixture of sand, clay, small stones, and fragments of bone must necessarily have been brought there by streams of water, or washed in by waves. And yet in many instances—perhaps in by far the great majority of instances—nothing can be imagined as much less likely to have happened than the aggregation of such materials by any means of that kind: that it should have been an occurrence of almost universal prevalence may well be deemed impossible. For under what circumstance can it be conceived that floods of water, in every region where open caverns exist in the rocks, should have picked up a heterogeneous collection of bones just in time to lay them quietly down again in every hole into which the muddy stream could gain access? For we must really suppose so well-timed an acquisition of future fossils, before we can admit the usually received hypothesis of the manner in which they were deposited where we find them; since no one can suppose that the whole of the solid matter borne along by any great flood—not to say by every such flood—could have been such as we observe so constantly in these bone-breccias.

In the year 1851 I read a paper before the Geological Society “On the Superficial Accumulations and Surface-markings in North Wales,” in which I attempted to show that there had been two glacier epochs in that country, one before, and the other after the deposition of the boulder drift, which was ploughed out of some of the larger valleys by the secondhand smaller set of glaciers; and in a later work on the old glaciers of North Wales, I went further, showing that cold sufficient to form glaciers lasted during the whole time of submergence and emergence, both when the higher mountain-tops stood out of the sea as a cluster ofsmall islands, and afterwards when the whole land rose out of the water.

The first of these memoirs touched on several subjects not immediately connected with the glaciation of Wales, though bearing in a larger sense on the same Geological period, and on the same set of questions. This the Council of the Geological Society decided not to print in their Journal, on the ground that it was too speculative—an opinion with which, in a great measure, I now coincide. One question was, however, raised in this unprinted matter which I do not yet remember to have seen in any published paper, and I now mention it because of late the attention of many persons have been more and more drawn to the discussion of the subject.