AGASSIZ: BERMUDAS. 223 



It is probable that the other non-calcareous rocks and minerals which 

 have occasionally been found may have been brought here by floating 

 trunks and roots of trees, as is tiie case in many of the oceanic islands. 

 We should, however, not forget the possibility of their being the frag- 

 ments of the volcanic summit around which the proto-Bermudiau reef 

 was first formed, a summit which has completely disappeared, either ow- 

 ing to subsidence or to disintegration, or to both combined. There exists 

 in the collection in the Government Building a piece of fine-grained 

 seolian rock of a reddish tint from the north shore near Warwick Road, 

 in which is embedded an angular fragment of basalt, or some eruptive 

 rock. 



For a coral island the elevation of tlie Bermudas is very considerable. 

 The highest points are Sears Hill, 260 feet, Gibbs Hill, 240 feet, and 

 Piospect Hill, 222 feet ; a number of points reach an elevation of 

 nearly 150 feet. On the Bahamas, with the exception of the highest 

 points of Cat Island, which are said to reach 400 feet, the greater num- 

 ber of tlie seolian hills do not rise to more tlian from GO to 100 feet, 

 very many of the islands attaining a height of not more than from 20 

 to 40 feet, and only a few summits reaching over 200 feet. But it 

 should be remembered that the heights named are not due to the ele- 

 vation of coral reef rock, but to the height attained by the asolian hills 

 which constitute the dry land of the two groups. 



The Bermudas and Bahamas ^ offer an example of the thickness that 

 a recent limestone deposit may attain during a period of rest. Assuming 

 for the Bernuidas a probable subsidence of 70 feet and a greatest ele- 

 vation of 260 feet, we get an asolian coral limestone of 330 feet in thick- 

 ness, the material of which has all come from a reef which itself was 

 ^probably not thicker than 120 feet, or a total thickness of 450 feet. 

 When we remember how readily these coral limestones are changed into 

 hard ringing rocks, we introduce a new element into the discussion of 

 the mode of formation of huge masses of limestone, especially in the 

 region of the trade winds. 



The beach rock and the so called base rock which have been observed 

 at the Bermudas belong, I believe, to tvvo different types. The former, 

 the beach rock, consisting of coral or other sand, is deposited in strata 

 dipping to the sea at a slight inclination, and is characteristic of all 

 coral reef districts where sand is accumulated along a shelving line of 

 coast. This frequently becomes hardened and changed to a ringing 

 limestone, and is composed usually of rather coarse particles, but not 



1 A. Agassiz, Bull. Mus. Comp. Zoiil., Vol. XXVI. No. 1, p. 183. 



