Geological Society. 307 



at by different modes of applying increasing or decreasing 

 temperature to the pile. All that now need be said on that 

 head is that I have thermo-electric piles varying from fifteen 

 to thirty pairs of metallic elements, which give brilliant sparks 

 by simply pouring hot water on one end, while the other end 

 is at the temperature of the atmosphere. Again, sparks are 

 exhibited by the same piles when the temperature is reduced 

 at one end by the aid of ice, and the other end at the tempe- 

 rature of the surrounding air. 



Of course, as has been noticed before, the effects will be 

 greatly enhanced by still greater difference of temperature 

 being produced at the opposite end of the pile. 



I remain, Gentlemen, yours, &c, 

 5, Charing Cross. FRAN CIS WATKI NS. 



XXXVIII. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



May 31, " tf^N certain areas of elevation and subsidence in 

 1837. ^~J the Pacific and Indian oceans, as deduced from 



the study of Coral Formations ;" by Charles Darwin, Esq., F.G.S. 

 The author commenced by observing on some of the most re- 

 markable points in the structure of Lagoon islands. He then pro- 

 ceeded to show that the lamelliform corals, the only efficient agents 

 in forming a reef, do not grow at any great depths j and that be- 

 yond twelve fathoms thebottom generally consists of calcareous sand, 

 or of masses of dead coral rock. As long as Lagoon islands were 

 considered the only difficulty to be solved, the belief that corals 

 constructed their habitations (or speaking more correctly, their 

 skeletons), on the crests of submarine craters, was both plausible and 

 very ingenious ; although the immense size, sinuous outline, and 

 great number, must have startled any one who adopted this theory. 

 Mr. Darwin remarked that a class of reefs which he calls «' encir- 

 cling" are quite, if not more, extraordinary. These form a ring 

 round mountainous islands, at the distance of two and three miles 

 from the shore ; rising on the outside from a profoundly deep ocean, 

 and separated from the land by a channel, frequently about 200 

 and sometimes 300 feet deep. This structure as observed by Balbi 

 resembles a lagoon, or an atoll, surrounding another island. In 

 this case it is impossible, on account of the nature of the central 

 mass, to consider the reef as based on an external crater, or on any 

 accumulation of sediment; for such reefs encircle the submarine 

 prolongation of islands, as well as the islands themselves. Of this 

 case New Caledonia presents an extraordinary instance, the double 

 line of reef extending 140 miles beyond the island. Again the Bar- 

 rier reef, running for nearly 1000 miles parallel to the North- East 

 coast of Australia, and including a wide and deep arm of the sea, 

 forms a third class, and is the grandest and most extraordinary coral 

 formation in the world. 



2 R2 



