112 J. LeConte— Critical Periods in the History of the Earth, 
and a far broader connection existed then than now. Through 
this open gateway came the fauna of South America, especially 
the great Edentates, into North America. Similarly a broad 
connection then existed between America and Asia in the 
regions of the shallow sea between the Aleutian Isles and 
Behring Straits. Through this gateway came an invasion from 
Asia, including probably the Mammoth. With this invasion 
probably came also Man. It seems probable, therefore, that 
the earliest remains of man in America will be found on the 
Pacific coast. 
lso the great Pliocene Lake, which stretched from near the 
shores of the Gulf far into British America, and possibly into 
Arctic regions, and formed a more or less complete barrier to 
the mammalian fauna east and west, was abolished by upheaval, 
and free communication was established. It is impossible that 
some Pliocene Autocthones isolated there by subsidence in 
Mediterranean region closing the southern gateways, and still 
exist there under slightly modified forms; the Arctic invaders 
were again driven northward by return of more genial climate, 
invasion came man, and was a prime agent in determining the 
final result. 
