204 The Naturalist in Nicaragua 
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 ice- 
bergs 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 Maran- 
ham, 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°, 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.” + 
There is another branch of the subject that I cannot so 
1] have since discussed this question in the Quarterly Journal of 
Science for October 1874. 
