communication in the tropics between the two seas since the close of the miocene period, whilst the connection that is supposed to have existed at that remote epoch, and to account for the distribution of corals, whilst advocated by Professor Duncan and other eminent men, is disputed by others equally eminent. No zoologist of note believes that there has been a submergence of the land lying between the Pacific and the Atlantic since the pliocene period, and icebergs could not have floated without such submergence, so that, in the cases I have mentioned, the boulders, if ice-borne, have been carried by glaciers and not by floating ice. Whilst I thus found evidence of the ice of the glacial period reaching, in the northern hemisphere, to within the tropics; in the southern hemisphere Professor Hartt has found glacial drift extending from Patagonia, all through Brazil to Pernambuco, and Agassiz has even announced the discovery of glacial moraines up to the equator. I have myself seen, near Pernambuco, and in the province of Maranham, in Brazil, a great drift deposit that I believe to be of glacial origin; and I think it highly probable that the evidence that is accumulating will force geologists to the conclusion that the ice of the glacial period was not only more extensive than has been generally supposed, but that it existed at the same time in the northern and southern hemispheres, leaving, at least, on the American continent, only the lower lands of the tropics free from the icy covering. I shall not enter upon the question of the cause of the cold of the glacial period. It is probably closely connected with the cause of an exactly opposite state of things, the heat of the miocene period, when the beech, the hazel, and the plane lived and flourished in Spitzbergen, as far north as latitude 78 degrees, and, according to Heer, firs and poplars reached to the North Pole, if there was then land there for them to grow upon. I consider that the great extension of the ice in the glacial period supports the conclusion of Professor Heer, founded on the northern extension of the miocene flora, that these enormous changes of climate cannot be explained by any rearrangement of the relative positions of land and water, and that "we are face to face with a problem whose solution must be attempted and doubtless completed by the astronomer."* (* I have since discussed this question in the "Quarterly Journal of Science" for October 1874.)