Origin of Mountains. 435 
This conclusion is further sustained by the known universal- 
ity of oscillations over the oceanic basin. The central Pacific 
area of coral islands—“ registers of sabsidence ”—stretches from 
the eastern Paumotus to the western Carolines, ninety 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 latest era of geological history. 
he above considerations sustain me in the opinion expressed 
in 1856 (this Journal, xxii, 335), that the relation in size be- 
tween the mountains and the bordering oceans is not merely 
“formal,” as pronounced by my friend Prof. LeConte, but has a 
dynamical significance. 
_ In view of the considerations here presented, I believe there 
18 no occasion to reject the fourth proposition (4 a) on page 424; 
but only to modify it as follows: 
4a, Owing to the general contraction of the globe, the greater 
size of the oceanic than the continental areas, and the greater sub- 
sidence 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, ¢here- 
fore, these borders within 300 to 1,000 miles of the coast, ete. 
5. Mountain-making slow work. 
and gentle oscillations. After the peng of the Primordial, 
the first period of disturbance in Nort 
the Silurian; so that the Appalachians were at least 35,000,000 
? 
of years in making, the preparatory subsidence having begu 
* These ti tes of the ewer onal 2 gth £ g + 
hess of their rocks—very in data, but the best we have. 
» A 
