434 J.D. Dana—Results of the Earth's Contractiun. 
I believe it to be a true cause. It is certain that the depressing 
of the ocean’s bed, like the raising of the continental areas, has 
been in progress through the ages. The great principal rise of 
the continent and continental mountains took place after the 
the mobile waters that occupy the oceanic depressions would 
have given important aid in the cooling of the underlying 
crust. It is to be noted, also, that the distance between the axis 
of the Appalachians in North America, and the opposite 
(African) side of the Atlantic is 4000 miles; and that between 
the axis of the Rocky Mountains and the opposite (Australian) 
coast of the Pacific is over 7000 miles, while between the axis 
of the Appalachians in Virginia and that of the Rocky Moun- 
tains in the same latitude, the distance is hardly 1500 miles. 
Hence the contraction was absolutely greatest over the oceanic 
areas, independently of any result from special causes; and i 
the generated pressure were not expended in uplifts over the 
oceanic areas themselves, it would have been in uplifts on 1ts 
borders. 
In addition to the above advantage which the oceanic areas 
. 
oceanic basin is generally above five degrees. 
_ _* The angle of slope on the sides of the Oceanic basin has not yet been properly 
investigated. The margin of the basin on the Atlantic border is now in about 100 
fathoms water (600 feet). According to soundings by the Coast Survey, as I am 
informed by Mr. A. Lidenkohl of the Coast Survey Office, through J. E. Hilgard, 
istant-i between 100 and 200 fathoms off Cape Hat- 
‘ 's Shoal, 1° 35’, But 
soundings off St. George's Bank indicate a slope of 
may be inferred that the slope rather increases 
fathom line.” 
