32 Mr J. D. Dana on the Volcanoes of the Moon. 



ing and actual elevations, and various oscillations of the con- 

 tinental surface, from subaerial to submarine, and the re- 

 verse. When contraction had once taken place over the con- 

 tinents, as v^ell as under the ocean, there may have after- 

 wards been expansions again through the return of heat 

 from some cause. And thus various irregularities have taken 

 place, such as the rocks indicate. In the tertiary period, and 

 since, the apparent rise of the land has been still to some ex- 

 tent in progress. And is there any evidence that this could 

 have arisen from a sinking of the ocean's bed ? The evidence 

 is undoubted. For Mr Darwin has shewn satisfactorily (and 

 farther observations to the same end, and to many interest- 

 ing conclusions, will be presented in the writer's Geological 

 Report on the Pacific), that a subsidence of some thousands 

 of feet has taken place since the corals commenced their 

 growth. Every coral island is a register of this subsidence.* 



And why should not the ocean's bottom subside, as well as 

 the land^ What has given tho continental portions of our 

 globe their elevation, as compared with other parts, if not 

 the unequal contraction of the whole ? Can we safely affirm 

 — in words of high authority — " that the stability of the sea 

 and the mobility of the land are demonstrated truths in geo- 

 logy,"! when mobile land forms also the bed of the ocean, 

 and its changes must affect the stability of the superincum- 

 bent waters ; — I ask, can we safely make this affirmation, un- 

 til we know something more certain than past investigations 

 have revealed, about the geological history of the two-thirds 

 of the surface of our planet that are concealed beneath its 

 oceans \ ^ 



In our conclusions from the above reasoning, we fall in 

 nearly with the views presented by a distinguished French 

 geologist, M. C. Prevost, who has argued with much force in 

 favour of subsidence as a cause of the apparent elevation of 

 the land ; though it may be right to state, that these conclu- 

 sions were arrived at previously to seeing his memoir.* There 



* See Silliman's Journal, xlv., p. 131, 1843. 



t Leonard Horner, Esq., Anniversary Address before the Geological Society 

 of London, January, 1846 ; Quarterly Jour, of the Geol. Soc, No. 6, p. 199. 



* The general theory of changes of level hy contraction and expansion, and 



