552 



the draft observed to pass down into the well. The whole of the 

 neighbouring district, to the extent of four miles, is called by the 

 well- diggers, foul country. Similar phenomena were observed in 

 digging a well on the opposite hill at Applebury, and also in form- 

 ing some wells in the immediate vicinity of London. 



May 31. — James Heywood, Esq., of Manchester ; Richard Owen, 

 Esq., F.R.S., Hunterian Professor in the Royal College of Surgeons, 

 London ; Robert William Mackay, Esq., of Lincoln's Inn ; and 

 Charles Humfrey, Esq., A.M., of Downing College, Cambridge; 

 were elected Fellows of this Society. 



" On certain areas of elevation and subsidence in 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 ; and that be- 

 yond twelve fathoms thebottom generally consistsof 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 outhne, 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 JOOO 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 grandestand most extraordinary coral 

 formation in the world. 



The reef itself in the three classes, encircling, barrier and lagoon, 

 is most closely similar ; the difference entirely lying in the absence 

 or presence of neighbouring land, and the relative position which 

 the reefs bear to it. The author particularly points out one diffi- 

 culty in understanding the structure in the barrier and encircling 

 classes, namely, that the reef extends so far from the shore, that a 

 line drawn perpendicularly from its outer edge down to the solid 



