330 
ORIGIN OF LIFE IN AMERICA-! 
of a low-lying plain. This district, moreover, is entirely 
granitic and composed of a number of high ridges running 
parallel in an east-westerly direction, the remainder of the 
great peninsula being largely formed of calcareous rocks with 
mountain ranges running in a north and south direction. 
Between the two lies a great plain several hundred miles long 
with a height of scarcely one hundred and fifty feet above sea- 
level. The two mountain ranges manifestly belong to entirely 
different systems, and the junction between the two must have 
been a comparatively recent geological event. Mr. Eisen* 
was so much impressed by the supposed severity of the climate 
during the Glacial Epoch that he believed the whole Cape 
region was at that time wrapped in snow and ice and devoid of 
animal life. But he also contends that it must have been an 
island and that during its rise animals and plants gradually 
reached it from the mainland by accidental transport. That 
the Cape Region has only recently become part of Lower Cali¬ 
fornia is highly probable. To judge from the fauna and flora, 
it must have been connected by land with some part of Central 
America or southern Mexico, though it possesses affinities, too, 
with Asia and the Pacific islands (compare, p. 208). Rather 
more than half-way across the sea between the Cape Region 
and the south coast of Mexico lies the small group of the 
Tres Marias islands, and it might be argued that they 
had once formed the connecting link between the mainland 
and that faunistically so remarkable Cape Region of Lower 
California. The animals and plants of these islands, how¬ 
ever, although clearly showing that the islands have been 
joined to one another and to southern Mexico, exhibit no 
near relationship to those of the Cape Region.f Hence it 
is probable that the faunistic and floristic affinity between 
the Cape Region and southern Mexico is due to the fact 
that both regions have acquired their animals and plants, in 
more remote times, from the same source in Central America. 
I suggested in a former chapter (p. 237) that the moun¬ 
tains of Guatemala had once extended further westward. 
Guatemala certainly seems to have been a land surface 
* Eisen, G., “ Explorations in the Cape Region,” p. 735. 
f Nelson, E. W., L. Stejneger, and others, “Natural History of the 
Tres Marias Islands.” 
