54 On some Results of the Earth's Contraction from Cooling. 



inevitably under the direction of the adjoining oceanic crust. 

 The angle of slope of the deep-water sides of the oceanic basin is 

 generally above five degrees*. 



This conclusion is further sustained by the known univer- 

 sality of oscillations over the oceanic basin. The central Pacific 

 area of coral islands ("registers of subsidence") stretches from 

 the eastern Paumotus to the western Carolines, 90 degrees in 

 longitude, and it indicates that the comparatively recent coral- 

 island subsidence involved a region stretching over more than 

 one fourth the circumference of the globe. The fact teaches 

 that the movements of the globe, which have been in progress 

 through all time in obedience to the irresistible energy generated 

 by contraction, have been world-wide, and so world-developing, 

 even down to the last era of geological history. 



The above considerations sustain me in the opinion expressed 

 in 1856 (Amer. Journ. Sci. 2nd ser. vol. xxii. p. 335), that the 

 relation in size between the mountains and the bordering oceans 

 is not merely "formal," as pronounced by my friend Professor 

 LeConte, but has a dynamical significance. 



In view of the considerations here presented, I believe there 

 is no occasion to reject the fourth proposition, 4 (a) on page 42, 

 but only to modify it as follows :— 



4. (a) Owing to the general contraction of the globe, the greater 

 size of the oceanic than the continental areas, and the greater 

 subsidence from continued contraction over the former than over 

 the latter, and also to the fact that the oceanic crust had the 

 advantage of leverage, or, more strictly, of obliquely upward 

 thrust against the borders of the continents because of its lower 

 position, therefore along these borders, within 300 to 1000 miles 

 of the coast, &c. 



[To be continued.] 



* 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, Esq., Assistant-in-Charge, the slope 

 between 100 and 200 fathoms off Cape Hatteras is 2° 31', off New York 

 entrance 2° 02', off George's Shoal 1° 35'. But for the region beyond 200 

 fathoms the data are not sufficient for any certain conclusion. Mr. Liden- 

 kohl observes: — "If the soundings by Lieutenant Murray off Cape Look-out 

 can be trusted, the slope between the 100- and 2000-fathom line must be 

 over 7 degrees. Berryman's soundings off St. George's Bank indicate a 

 slope of about 3^ degrees. From this it may be inferred that the slope 

 rather increases than decreases beyond the 200-fathom line." 



