514 Transactions. — Miscellaneous. 



places, just as we see that there are very great differences 

 now in climate between places in the same latitudes but 

 under different conditions as to heights above the sea, 

 moisture, and the vicinity of cold or warm ocean-currents, 

 &c. With these explanations I may confidently assert that 

 it is a fact, supported by such a mass of geological evidence 

 as to put it beyond the possibility of doubt, that there was a 

 time in this world's history — comparatively recent from a 

 geological point of view — when climatic conditions somewhat 

 resembling those now existing in Greenland and other arctic 

 and antarctic regions extended very much farther south in the 

 Northern Hemisphere, and also very much farther north in 

 the Southern Hemisphere, than at present. It is, perhaps, not 

 yet quite certain that this glacial condition in the Southern 

 Hemisphere was synchronous with the glacial condition in the 

 Northern Hemisphere, but I believe that the geological evi- 

 dence is in favour of this conclusion. This remarkable fact 

 in the history of our globe has given rise to much speculation, 

 inquiry, and discussion. The questions to be solved were 

 three: 1. When did this ice age terminate? 2. How long had 

 it lasted ? 3. W nat was the cause which produced it, and why 

 did this cause cease to act ? In no part of the world has the 

 ice age left its record so completely and on so grand a scale as 

 in North America. The record has there been studied most 

 carefully and exhaustively ; and fortunately there are in that 

 country several cases in which rivers, which, from the circum- 

 stances of the case, could not have been flowing during the ice 

 age, have cut back new channels at waterfalls, since the dis- 

 appearance of the ice, for distances which, when compared 

 with the rate at which the edges of the w T aterfalls have retro- 

 graded during recent times, give a fair measure of the time 

 during which these rivers have acted, and therefore of the 

 date when glacial conditions ceased there. The Niagara Falls 

 is the best known of these instances ; but falls on the Missouri 

 at St. Anthony and on other rivers have given similar evidence ; 

 and the general result arrived at is that the glacial condition, 

 both in North America and in Europe, terminated from 10,000 

 to 8,000, or even less, years ago. The duration of the glacial 

 condition has been estimated approximately by American 

 geologists at from 12,000 to 24,000 years, and by Professor 

 Prestwich at from 15,000 to 25,000 years. These latter are 

 wide margins ; but the data, chiefly the masses of moraine 

 left by the retreating ice, and the distances travelled by 

 erratic boulders compared with known rates of glacier motions, 

 are so imperfect that probably no nearer approximation can 

 be made geologically. The theory of two separate ice ages in 

 succession has been upheld by some ; but it is now discredited 

 in America, the appearances which seemed to indicate these 



