ORIGIN OF THE ANDES 
23 
from Ecuador to Chile, which had invaded the region from the 
Argentine plains. This circumstance also shows the lack of 
efficient barriers at that time to prevent dispersal, as does also 
the presence of vegetation sufficient to sustain the enormous bulk 
of the ground-sloth and similar giant vegetarians. 
This differential movement is shown by the enormous thickness 
of late Pliocene or early Pleistocene, of many thousand feet of 
apparent thickness (probably slope deposition) found on the 
altaplanicie and east of the Front Range in Bolivia. Continued 
elevation of the mountain segments in the late Pliocene, of early 
Pleistocene, resulted in the formation of mountain glaciers, canon¬ 
cutting and valley-filling. 
There has been some elevation of the mountain segments in 
post-Glacial time, resulting in cutting off the supply of precipita¬ 
tion from peaks which were once snow-clad, and in the very youth¬ 
ful box-canons and valley-gorges of intrenched streams, the un¬ 
graded river-beds and the recently dissected mature slopes, e. g. 
east of La Paz. 
Summing up the evidence that major uplift of the Andes was 
post-Miocene in point of time, it may be stated, that, 
(1.) There was measurable change in climate, largely due to 
altitude shown by the Pliocene fossil floras of Jancocata, Coro- 
coro, Potosi, Pisllypampa and other localities in Bolivia, where 
plants which could not live above 5,000-6,000 feet are found in 
fossil state at elevations ranging from 11,800 to 13,500 feet. 
(2.) There is abundant evidences of the existence of fault- 
scarps along Pacific Coast, along the Andean Front Range,^^ and 
along the Front Range of Bolivia (as observed by Mertie and 
others), in southern Chile, and between the Andes and the pre- 
Cordillera in Argentina. 
(3.) There are antecedent streams of Peru and Bolivia which 
flow to the Atlantic ocean, and those of southern Chile which reach 
the Pacific. 
(4.) Cape Fair weather oyster beds of Patagonia, which are 
at sea-level along the Straits of Magellan, rise to elevations of 
over 5,000 feet in the Andean spurs of Patagonia, as observed by 
Hatcher. ^ 
(5.) Recent dissection of mature topography and the dis- 
13 Recorded by I. Bowman. 
