LIFE IN THE PAST 167 
Eozoic time for us to assert with any positiveness that 
the ancestral habit is responsible for this trait in the 
descendants. Sure it is that to-day our cells, like their 
ancestors of old, live in water, and this water is 
slightly salty—as were probably the Archzan seas. 
The geologist tries as best he may to build up the 
geography of the earth in the past. He endeavors to 
judge from the rocks as he now finds them, where the 
seas, the bays, the dry land, and the mountains of 
earlier geological times lay. The present aspect of 
the earth is very recent, and earlier ages must have 
shown an entirely different distribution of land and 
water. The North American continent was certainly 
very much smaller than it is now. The first known 
lands lay close to the Atlantic seaboard and probably 
extended out into the water some distance beyond the 
present shoreline. The stretch of continent was nar- 
row, and grew narrower as it went southward. In 
what is now the Canadian district, a considerable 
expanse probably existed in very early times. Then 
a great internal sea, shallower than the Atlantic, 
stretched its unbroken sheet over almost the entire 
area now occupied by the United States, while only a 
comparatively small hump of earth, ending in a nar- 
rower strip, lay where the great Western plateau now 
rears its enormous bulk. 
A large portion of the history of the North Amer- 
