WARREN UPHAM, ESQ., ON CAUSES OF THE ICE AGE. 209 



eccentricity 240,000 to 80,000 years ago was coincident with 

 great altitude of north-western Europe, North America, 

 and Patagonia, which consequently became covered by ice- 

 sheets ; but that such previous times of eccentiicity, not 

 being favoured by geographic conditions, were not attended 

 by glaciation. The recentness of the Ice age, however, 

 seems to demonstrate that eccentricity w^ns not its primary 

 cause, and to bring doubt that it has exerted any determining 

 influence in producing unusual severity of cold either during 

 the Pleistocene or any former period. 



16 In various localities we are able to measure the present 

 rate of erosion of gorges below waterfalls, and the length of the 

 postglacial gorge divided by the rate of recession of the falls 

 gives approximately the time since the Ice age. Such 

 measurements of the gorge and Falls of St. Anthony by 

 Prof. N. H. Winchell show the length of the Postglacial or 

 Recent period to have been about 8,(t0i) years ; and from the 

 surveys of Niagara Falls. Mr. G. K. Gilbert believes it to have 

 been 7,000 years, more or less. From the rates of wave- 

 cutting along the sides of Lake Michigan and the consequent 

 accumulation of sand around the south end of the lake. Dr. 

 E. Andrews estimates that the land there became uncovered 

 fi-om its ice-sheet not more than 7,500 years ago. Prof. G. 

 Frederick Wright obtains a similar result fi'om the rate of 

 filling of kettle-holes among the gravel knolls and ridges 

 called k-imes and eskers, and likewise from the erosion of 

 valleys by streams tributary to Lake Erie; and Prof. Ben. 

 K. Emerson, from the rate of deposition of modified drift 

 in the Connecticut valley at Northampton, Mass., thinks 

 that the time since the Glacial period cannot exceed 10,000 

 years. An equally small estimate is also indicated by the 

 studies of Gilbert and Russell for the time since the last 

 great rise of the Quaternary lakes Bonneville and Lahontan, 

 lying in Utah and Nevada, within the arid Great Basin of 

 interior drainage, which are believed to have been contem- 

 poraneous with the great extension of ice-sheets upon the 

 northern part of the North American continent. 



17 Prof. James Geikie maintains that the use of palolitliic 

 implements had ceased, and that early man in Europe made 

 neolithic (polished) implements, before the recession of the 

 ice-sheet from Scotland, Denmark, and the Scandinavian 

 peninsula; and Prestwicli suggests that the dawn of civiliza- 

 tion in Egypt, China, and India, may have been coeval with 

 the glaciation of north-western Europe. In Wales and 



p 2 



