'/ Ultwial Epoch at the Eijitatur. 303 



4°*. I5ui Ixtwrcii IVbas and Pant, a .listaiioi; i»f KJOO miles, 

 the slope is only S' ;">", or about '1\ indies per mile; and tVoni 

 the tij)-to|> of the iVndis to the Atlantie the inelination is 

 C 30". Ue eonelude, therefore, that if a sheet of iec ever 

 spread from Cotopaxi to the mouth of the Amazon, it remained 

 there, immovable as the mountains. 



IJut ditlieidties lie beyond this. As the lenf,^th of a glaeicr 

 denends <;reatly upon the speed with whieh it travels, it 

 will be short in jirojjortion as the angle of the slopi' is diiiii- 

 nished. And, turther, supjxtse the iee-sheet fornuMl nnil 

 moving, what would be its How ? Even if its rate erpialK-d 

 that of the Mer de Glace, a boulder from the Andes would be 

 over 20,000 years in reacliing the Atlantic; but wluii we 

 consider its feeble slope, and its retardation l)y the eonstant 

 trade-winds, we may wonder if it ever completeil its journiy. 

 Yet this Agassiz glacier is represented as doing a greater 

 amount of work than the high-latitude ghiciers, grinding up 

 and covering the vast basin with 800 feet of detritus, '' the 

 most colossal drift formation known." Ami, again, all the 

 slone of any consequence lies between the axis of the Andes 

 ana Pebas, a distance of 450 miles. In this abrupt descent 

 (35 feet per mile) it must receive momentum to carry it over 

 an almost level plain of IGOO miles. Why did it not |)lougli 

 up tlie silt, creating linear lakes like Como and Maggiore, 

 whicii radiate at right angles to the strike of the Alps'/ Yet 

 there is no appearance of excavation. The laguncs of the 

 Napo are shallow ponds. 



4. The existence of such a continental glacier at the equator 

 would profoundly aifect the life-history of the globe. As 

 Newberry says, " Nearly all the fossil plants and mollusks of 

 the strata deposited immediately anterior to the glacial epoch 

 are undistinguishable from species now living in the same 

 region"t' If a mantle of ice ever covered Amazonia, un- 

 doubtedly it had lateral branches descending the valleys of 

 the Orinoco and Paraguay : there is a close similarity of the 

 formation in these valleys to the Amazonian clay, which has 

 resulted, Ave thiidc, from a conteni])oraneousncss, if not identity, 

 of origin ; and so low is the watershed, especially on the north, 

 that the two river-systems are joined by natural canals J. 



* Tlie average slope of the Mer de Glace is 14°, that of the Greenland 

 glacier IP. 



t In the opinion of De Candolle, subscribed to by Gray as likely, the 

 greater part of the existing species of plants are older than the present 

 confifiin-atioii of our contint-nt. 



\ The Casiquiari is only 400 feet above the sea, or about 200 above the 

 centre of the Amazon basiu. 



