200 
ORIGIN OF LIFE INJ AMERICA 
of view, how far westward and southward of the Gulf of Cali¬ 
fornia did this land extend ? No Cretaceous or Tertiary- 
deposits have yet been discovered on the greater portion of 
the Pacific coast of Central America. Geological evidence is, 
therefore, rather in favour of the supposition that this western 
land formerly extended further south. 
As regards the present arid semi-desert conditions of 
Arizona and New Mexico, they supported in early Tertiary 
times, as I have already mentioned, a wealth of animal 
life. In the neighbouring state of Colorado the wonderfully 
preserved impressions of' insects in the volcanic tufts of 
Florissant, which have been described by Dr. Scudder and 
more recently by Professor Cockerell,* leave no doubt as to the 
former climatic conditions of that part of America and its 
suitability for plant and animal life. The vast outpouring 
of lava and general volcanic disturbance in the Rocky Moun¬ 
tain region continued through Miocene and partly through 
Pliocene times. All the same, the immigration of tropical 
types of mammals from South America into the Western 
States at that time would seem to imply the existence in the 
latter of a luxuriant flora. Even in Pleistocene times an 
abundance of large mammals, such as elephants and masto¬ 
dons, existed in southern California, and probably in the 
neighbouring States, to judge from the number of sabre¬ 
tooth tiger remains recently discovered in the asphaltum 
beds of Rancho la Brea near Los Angeles. The gradual 
desiccation noticeable in some of the south-western States 
is obviously a recent development, though the abundance 
and diversity of cactuses and of reptiles adapted to a desert 
life imply that local arid areas must have existed for long 
ages past. 
If the geological history of the extreme south-west of North 
America has been correctly interpretated in this very brief 
summary, we should certainly find relicts of ancient animal 
and vegetable types in some of the western areas that have 
remained unsubmerged during Tertiary times. For although 
most animals would tend to spread from these old centres as 
new land became available for their dispersal, some of the 
Cockerell, T. D. A., “ Fossil Fauna and Flora of Florissant.” 
