1886. } some of its Apparent Causes. 35 
and Pacific coast. The tropical flora and fauna now confined to 
the neighborhood of Guyaquil on the coast of Peru then probably 
spread over Bolivia, Ecuador, Peru and Chili to Patagonia. The 
tropical belt in Peru ends with the chinchona forests of Loja, which 
is 6768 feet above the Pacific ocean. The sugar cane grows in 
Baños which is about 6500 feet high. At Riobamba, with an 
elevation of 9200 feet, the climate and vegetation are temperate ; 
here occur bones of the mastodon, horse, deer and Ilama—animals 
which may have lived in a temperate climate. But was not their 
extinction, and that of the colossal sloths, armadillos, and other 
animals of the pampas largely due to a change of climate result- 
ing from the elevation of the Andean plateau ? 
As the land gradually rose, the atmosphere would become more 
rarified and insupportable to tropical life ; the animals and plants 
would either seek lower levels or undergo extinction, or in certain 
cases become modified into species suited to a temperate climate. 
As the plateau rose still higher, the air would become too cold 
and rarified for even the mastodon and horse. Gradually an alpine 
zone became established, and finally the higher peaks of the Andes, 
at an elevation of 15,000 feet, became mantled with perennial snow, 
and on the eastern flanks of Chimborazo, which intercepts the 
moisture of the Atlantic trades, glaciers established themselves. 
We thus see how, within Quaternary times, temperate and alpine 
zones became established over the vast Andean plateau, originally, 
perhaps at the end of the Pliocene, a plateau of the third order, 
clothed with vast forests like those of Brazil and Venezuela. 
In Patagonia, likewise, the elevation of the Cordillera, and the 
change of level of the low lands of the eastern coast, now well- 
known to have happened, are they not sufficient to account for 
the extinction of the fauna of the pampas ? 
The same phenomena obtained in Western North America. 
Throughout the Tertiary period there was in the northern portion — 
of the plateau region a secular rise of land, if not at times parox- ~ 
ysmal, resulting in the drainage of the plateau into the Pacific and 
the formation of vast inland seas and estuaries which eventually 
became fresh-water lakes. 
During the Laramie epoch the Rocky mountain plateau be- 
came dry land, and the elevation and drainage went on during the 
Eocene. The Gulf of Mexico was much larger in the Eocene 
epoch than now; afterwards the coast of Texas rose from 300 
