598 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



" Prof. Ramsey has given me (says Darwin), the maximum 

 thickness, in most cases from actual measurement, in a few cases 

 from estimates, of each formation in diiferent parts of Great Brit- 

 ain, and this is the result: 



Feet. 



Pala?zoic strata, not including igneous beds 57,150 



Secondary - 13,190 



Tertiary _ - --.--- 2,240 



Making nearly thirteen and three-fourths British miles." 



Again, Darwin says: " I am convinced that all our ancient for- 

 mations which are rich in fossils, have been formed during subsi- 

 dence. Since publishing my views on this sul>ject in 1845, 1 have 

 watched the progress of geology, and have been suriDrised to notice 

 "^how author after author in treating of this or that formation, has 

 come to the conclusion that it was accumulated during subsidence." 



Mr. Dana thinks there is proof that a portion of the Apalachrau 

 region subsided not less than seven miles, before it was elevated 

 to its present position. 



Sir John Herschell and Mr. Babbage have suggested that possi- 

 bly the weight of the sediment, derived from the abrasion of the 

 shores by the ocean currents, may, in some places, produce depres- 

 sions of the ocean's floor and crowd the subjacent lava up under 

 the dry lands, thus producing volcanoes, and perhaps adding to 

 the elevation of lands alrcad}^ raised above the sea. They have 

 not proposed to account in this way for the original formation and 

 elevation of the continents, nor have they pointed to any particular 

 locality which they propose to prove to have been elevated in this 

 manner. They have merely thrown out the idea as a plausible 

 conjecture, which is not inconsistent with known facts, nor with 

 dynamical principles. Mr. James Hall, the distinguished geolo- 

 gist of New York, in his latest official report, has expressed his 

 approval of this speculation. 



Without knowing anything of the opinions expressed by these 

 distinguished authors, I was led to the conclusion that all eleva- 

 tions, including the continents, were caused by the weight of 

 oceanic sediment. T inferred it from the remarkable relation? 

 which I found to exist between the directions of the currents and 

 of the shores, and also the relative positions and number of the 

 oceans and continents. 



It should be remarked, that if it were perfectly demonstrated 

 that the weight of the sediment had produced depressions, and 

 consequent elevations, this fact alone would be of little value; 



