GEOLOGICAL CONCLUSIONS. 117 



VIII. It is an inquiry of some interest, whether, in an archi- 

 pelago like the Paumotus, coral debris is not carried from the 

 coral islands, and distributed over the bottom of the ocean ; and 

 whether limestones thus originating, are not in process of forma- 

 tion. I venture no positive assertion on this subject, yet would 

 express strong doubts. The fact that soundings off some high 

 islands, as we recede from the reef-growing depths, lose more 

 and more in the proportion of coral sand, till we finally reach a 

 bottom of basaltic earth, like the material of the island, bears 

 against any such hypothesis. This was found to be the case off 

 Upolu, where the reefs are extensive. 



The action of the waves tends to throw back the material 

 washed into the sea by fresh water streams and other currents, 

 and in this manner extensive shore or shallow-water accumula- 

 tions have been formed in all ages of the world. The formation 

 from land debris of deep sea deposits, outside of soundings, is an 

 hypothesis of geologists, yet to be proved. Such results may 

 perhaps take place off the mouths of large rivers like the Amazon, 

 the force of whose currents carries their transported material far 

 to sea ; but not, it would seem, in any case where the streams 

 are small, or where the river current can not be traced out to 

 sea much beyond soundings. 



It remains still to speak of the proofs of elevation or subsi- 

 dence presented by coral islands throughout the Pacific, and of 

 the former extent of Pacific lands compared with the present. 

 But these topics relating to the dynamics of the ocean, form a 

 separate chapter. 



We might dwell also on the formation of caverns by the rains 

 becoming subterranean waters; on the illustration of the action 

 of marine currents afforded by this subject ; on the agency of 

 polyps in rock-making. But the deductions are too obvious to 

 require farther remark. 



of ammonia and leaves the lime as a soluble hydrate, which remrins united with the 

 carbonate of lime, forming a compound like that indicated as existing in mortar by 

 Fuchs; the final removal of the water by evaporation leaves the rock in a crystal- 

 lized state. For a full statement of this author's views, see the American Journal of 

 Science, [2], xiv, 245, and for a criticism on the same, ibid., p. 410. 



