Lieut. Nelson on the Geology of (he Bermudas. 121 



Building Materials. 



The Bermuda rock is much whiter than the ' Bath stone.' Blocks of any ordinary size and 

 strength can be obtained. The softer kinds, weighing at an average about ninety-five pounds 

 per cubic foot, with a cohesive strength equal to only a quarter that of brick, are quite strong 

 enough for house walls, where no great skill is required from the stone-mason. The houses are 

 in general roofed with thin slabs of this material, which admit rain unless secured by proper 

 washes. 



The harder sorts, like those of which the eastern half of Ireland Island is composed, vary in 

 specific gravity from 1600 to 2560. In raising tliese, powder must be employed; and the usual 

 tools for hard stone, in their conversion into ashler. In large masses, such as escarps, wharf 

 walls, &c., it generally answers tolerably well ; but it scarcely deserves a very high reputation, 

 from the cracks which the unequal composition of the stone occasions, when under very heavy 

 pressure. 



It is too pure to afford a good lime for external purposes, as it takes a long time to harden in 

 thick walls. Equally good lime is manufactured from all descriptions of stone found in the island, 

 regulating the choice by such localities as determine the economy of tlie burning process. 



The Bahamas. 



Judijing- by hand specimens^ from such repoits as I have been able to 

 collect^ from their form as given by the best maps^ and their position with 

 reference to the gulf of Mexico, I think it highly probable, that the Baha- 

 mas were produced by the same causes as those to which the Bermudas owe 

 their existence. 



I have been told on respectable authority, that the red earth is to be found 

 on the coasts of Florida. I have also seen specimens of Menacchinite from 

 the shores of Virginia. 



Concluding Remarks. 



Amongst the different speculations on the origin of coral groups, none are 

 more common than such as would effect the whole by plutonic action ; but 

 I can see no proof that tiie islands, though once formed beneath the surface 

 of the sea, were suddenly and subsequently elevated. The peculiar arrange- 

 ments of the strata, both in the mass and detail, and the constant occur- 

 rence of the Helix, appear to be conclusive against the above theory ; and if 

 dislocations of strata do occur, in only one instance (fig. 13, p. 118) are they 

 to be met with to an extent like those, which I have seen in the chalk near 

 Dover, and at Alum Bay, and due to undermining of the strata. 



In most notices on the Sunderbunds, it is stated, that islands are rapidly 

 formed around any nucleus, such as the trunk of a tree in the bottom of the 

 river, &c., which, reducing the velocity of the current, affords it the op- 



VOL. v. — SECOND SERIES. R 



