THE CAUSE OF THE GLACIAL PERIOD. 517 



the Permian period ended with disturbance and mountain- 

 building along a somewhat irregular west-to-east course through 

 southern Ireland, Wales, England, northern France, Belgium. 

 Germany, and southern Kussia ; * and it is to be remarked 

 that this European orographic line lies approximately in the 

 same great circle with the Appalachian ranges, both being in- 

 cluded by an arc of ninety degrees. Transverse to this circle 

 the Sinian Mountain system of eastern Asia was formed in the 

 same epoch, stretching from southwest to northeast along the 

 border of the Old World as the Appalachians similarly bound 

 our own continent.! Each of these mountain systems was 

 perhaps much longer than the extent now remaining, and each 

 has been reduced by erosion to only moderate heights ; but it 

 is not improbable that their altitude originally was like that 

 of the loftiest ranges of the world, some of which have been 

 formed and the others much uplifted during tbe last geologic 

 period. 



The shortness of the time that has elapsed since the latest 

 glaciation of North America, according to the observations 

 and computations of N. H. Winchell, Andrews, Wright, and 

 Gilbert, shows that this cold epoch was not coincident with 

 the period of eccentricity of the earth's orbit, which is regarded 

 by Croll, Geikie, and Wallace as the primary cause of the Ice 

 age. Eccentricity, therefore, had no share in producing this 

 most recent glaciation, which was more intense and severe, 

 and probably more sudden and brief, than the earlier very cold 

 epoch of the Ice age, as indicated by comparison of the mo- 

 rainic and other drift deposits. Furthermore, it seems proba- 

 ble that the Quaternary Glacial period, including its two or 

 more epochs of glaciation, each subdivided by episodes of tem- 

 porary retreat and readvance of the ice, besides the principal 

 interglacial epoch of warm or temperate climate, and perhaps 

 complete departure of the North American ice-sheet, was 

 wholly subsequent to the maximum eccentricity which the 



* Prestwich's " Geology," vol. i, p. 300. 



f " Geological Researches in China, Mongolia, and Japan," by Raphael Pum- 

 pelly, " Smithsonian Contributions," vol. xv, 1867, chap. vii. The conclusions 

 reached by Pumpelly concerning this mountain system are fully confirmed by 

 the subsequent gr:ind work of Baron Richthofen on the geology of China. 



