264 James Geikie — On Changes of Climate. 



in any numbers at the very surface; and their remains occur in 

 greatest profusion in the regions which have not been reached by 

 the drift. 



This anomalous distribution of the extinct mammalia appears in- 

 explicable on the assumption that the ossiferous beds are all of 

 postglacial age ; but if they belong for the most part to interglacial 

 times, the mode of their occurrence is precisely what might have 

 been expected. It seems indeed impossible to resist the conclusion 

 that at the time the mammalia frequented the lower latitudes of 

 Europe (where their remains occur so abundantly in river-gravels 

 and cave-deposits), and while mammoths, horses, buffaloes, and oxen 

 roamed over northern Siberia — Scotland, Ireland, Denmark, Scan- 

 dinavia and other regions of Northern Europe also supported an 

 abundant mammalian fauna, and that the mastodon and its congeners 

 likewise occupied what are now the wooded regions and barrens of 

 North America. And the remains of these creatures seldom or 

 never occur in the regions referred to, because either the deposits 

 which once contained them have been obliterated by the action of 

 ice, or are covered up and concealed by drift accumulations. 



Hitherto no reference has been made in these papers to Mr. CroU's 

 theory of the physical cause of changes of climate during geological 

 epochs. That theory for the first time rendered possible the recon- 

 ciliation of apparently contradictory facts. Phenomena which had 

 refused to be explained by any number of ingenious hypotheses 

 suddenly seemed to yield their secret, and the great " Age of Ice " 

 appeared all at once in a new light. The results of recent research 

 in this and other countries tend more and more to show that the 

 indirect influence of excentricity of the earth's orbit is the prime 

 cause of cosmical changes of climate. It was in 1864 that Mr. 

 CroU's first paper upon this subject appeared. At that time very little 

 was known about interglacial periods. Eamsay had already shown 

 that as regards Britain there had been two periods of great extension 

 of glaciers separated by an intervening age of submergence and 

 floating-ice. Morlot had also pointed out that the morainic deposits 

 of Switzerland gave evidence of the former existence of two ice 

 periods, and his results had subsequently been remarkably con- 

 firmed by Professor Heer, and others.^ But these later observa- 

 tions were certainly not geaerally known in Britain at the time 

 when the theory I refer to was published. It was, however, a 

 familiar fact that interglacial beds occurred in the till of Scotland, 

 and from the appearance of these deposits my brother had inferred 

 that the great ice-sheet occasionally melted away so far as to uncover 



^ I learn from Mr. A. E. Jornebohm, of the Geological Survey of Sweden, that in 

 that country there are two Tills, both of which he considers to be true moraines de 

 fond. He says that " the line of demarcation between them is generally very sharp, 

 and in some places the lower till has evidently been partly broken up, and denuded 

 before the upper till was deposited." " These facts," he continues, " seem to point 

 out that during the glacial period there was a great interval of comparatively mild 

 climate, when the ice retreated to the mountain regions ; the land, however, was not 

 submerged. Freshwater and superficial deposits that gathered during that interval 

 may have been completely destroyed by the returning ice." 



