200 ORIGIN OF LIFE IN! 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 tuffs 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." 



