THE GEOLOGY OF BERMUDA. 7 



tinned north-eastward by St. George's and David's Islands. The south- 

 western extremity of the Main Island bends around towards the north, 

 and the curve is thence continued northward and north-eastward by the 

 islands Somerset and Ireland. The hook-like south-west extremity of 

 the Main Island, with its continuation in Somerset and Ireland Islands, 

 incloses a lagoon called Great Sound. Two other lagoons are included 

 within the chain of islands on the southeast side of the ellipse : namely, 

 Harrington Sound, inclosed entirely by the Main Island, and commu- 

 nicating by a passage not exceeding 50 feet in width with the great 

 elliptical lagoon inclosed by the outer reef; and Castle Harbor, inclosed 

 by the eastern end of the Main Island, St. George's, David's, and sev- 

 eral smaller islands. The central part of the Main Island is occupied by 

 a peat-bog. The surface of this part of the island is elevated but little 

 above the sea-level ; and the peat, as I am informed by General Lefroy, 

 extends to a depth of 40 or 50 feet below the sea-level— a depth about 

 equal to that of the great lagoon inclosed by the outer reef. This bog 

 appears to mark the situation of a small lagoon now entirely filled up. 



The surface of the land is considerably diversified, though nowhere 

 attaining any great elevation. The highest hills are only about 250 feet 

 above the level of the sea. 



In consequence of the small extent of the land both horizontally and 

 vertically, and the extreme porosity of the rock of which it is composed, 

 there are no springs, streams, or lakes of fresh water in the islands. 

 The rain that falls, where it is not collected in artificial tanks, soaks 

 down into the porous rock until it mingles near the level of the sea with 

 the salt water with which the lower parts of the rock are saturated. 

 The water in the ponds and marshes, which occupy considerable areas 

 in the less elevated parts of the islands, is always brackish. The in- 

 habitants depend for their supply of water chiefly on the collection of 

 rain in tanks. These tanks are connected not only with the roofs of the 

 houses, but with areas on the hillsides scraped smooth for that purpose. 



The chain of islands is bordered on the south-east by a fringing reef, 

 distant perhaps a quarter of a mile on the average from the shore. On 

 the north side of the ellipse the line of the reef is nearly continuous; 

 but the only dry land is the little islet, or group of islets, the largest of 

 which, called North Rock, is about 8 feet in diameter and about 14 feet 

 in height. 



Along the course of the reef are numerous rings of calcareous rock, 

 a few feet or yards in diameter, rising to a level of about 2 feet above 



