PHYSICAL PROPERTIES OF THE TERTIARY. 
CONDITIONS AT BEGINNING OF TERTIARY TIME. 
At the beginning of Tertiary time the American continent seems 
to have had almost the size and shape it now has excepting a narrow 
border along the Atlantic and Gulf lines and a small area extend- 
ing up the Mississippi to near the mouth of the Ohio river. The 
great inland sea area which existed throughout Cretaceous times 
between the Rocky mountains and the Mississippi valley had been 
changed to dry land. The accompanying map, Plate XXV, shows 
the geography of the United States at the beginning of Tertiary 
time. It was the whole of the United States minus the parts marked 
as Tertiary lying along the Gulf of Mexico, the lower Mississippi 
valley, and the Atlantic ocean. The great inland Tertiary area, as 
will shortly be seen, was dry iand, while the Tertiary areas along 
the ocean boundaries were still under water. 
The degree of elevation which occurred in the west central part 
of America at the close of Cretaceous time is difficult to determine 
with exactness. It is probable, however, that the Rocky mountain 
area was elevated permanently above ocean water and to a sufficient 
hight to give a decided drainage in various directions. 
The Tertiary of America may well be divided into two classes; 
one, which was deposited under ocean water on the Atlantic and 
Gulf border areas; and another which was deposited by rivers and 
under lake water on the great inland area, including all of the inland 
plains Tertiary and the various Tertiary formations in different 
places in the Cordilleras. The elevation of the mountainous area 
was therefore sufficient to cause a great spread of mountain debris 
in many directions. The lesser areas in the valleys of the moun- 
tains were occupied probably by fresh water lakes, and as the 
descent fom the mountain sides was rapid the accumulation of sedi- 
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