CHANGES OP CLIMATE DURING GEOLOGICAL PERIODS. 77 



THE CHANGES OF CLIMATE DUEING GEOLOGICAL 

 PEBIODS.* 



BY THE REV. J. WILSON COOMBS, B.A. 



It has long been observed that the climate of the northern 

 hemisphere must — at a former and comparatively recent period — have 

 been considerably warmer than it is at present. The traces alike of the 

 fauna and flora discovered in the rocks, as well as the bones of animals 

 found in caves, and the fossil trees imbedded in the coal measures and 

 elsewhere, furnish undoubted evidence that at one time the climate in 

 this and other northern countries must have been nearly, if not wholly, 

 tropical. For many years geologists were satisfied with the explanation 

 that this reduction of temperature (which was supposed to have been 

 continuous and unbroken) was to be attributed to the gradual cooling of 

 the earth. But not to say that the effect of this upon climate is very 

 much smaller than was formerly supposed, the abundant evidence 

 which now exists of a much colder climate in former times than 

 that which at present obtains has rendered this theory no longer 

 tenable. 



The knowledge of glacial action in Norway and Switzerland, resulting 

 from the labours of Agassiz. Forbes, Tyndall, and others, has sufficed to 

 prove that not only were existing glaciers at one time much more 

 extensive than at present, but that in Alpine regions and elsewhere 

 glaciers were at one time present where now not even the most attenuated 

 ice-stream is to be seen. Moreover, the careful examination of the rock- 

 basins which form so many of the lakes of Switzerland led to the conclu- 

 sion that these must have been to a great extent hollowed out by the 

 continuous action through long ages of glaciers, vastly larger than those 

 which in regions more or less remote now supply the streams or rivers by 

 which these lakes are fed. Along with tbese discoveries the fact was 

 brought to light that there were abundant traces of ice-action in Britain 

 and in other lands where glaciers have certainly never been present in 

 historic times. Agassiz, Buckland, and others stated their belief to this 

 effect, but these statements attracted at the time but little attention. 

 Professor Bamsay discovered such traces in many parts of the Snowdon 

 range, and I13 and others bave found in the north of England and in 

 Scotland all the signs which in Switzerland have been observed to 

 indicate the presence of a glacier. " The Great Ice Age," by Mr. James 

 Geikie, furnishes an exhaustive account of what has hitherto been 

 brought to light by these investigations. Striated rocks, the roches 

 moutonnees, glacial moraines, and boulder clay or till are found in many 

 places and in great abundance, and, as in Switzerland, so also in Britain, 



*Read before the Cheltenham Natural Science Society, December 18th, 1879. 



