STRUCTURE OF THE TURKS ISLANDS 259 



the theory of Agassiz is that the foundations of the aeolian sandstone 

 would lie far beneath the surface of the sea. I find no reference in 

 his pages to the exposure of any base-rock in this region, and his 

 views would expressly exclude the idea of the existence of a founda- 

 tion of " reef-rock " at or above the sea-level. In the case of the 

 same aeolian formation in the Bermudas, Professors Heilprin and 

 Rice lay stress on the exposure of a foundation of reef-rock; but 

 Agassiz rejects their interpretation. Naturally, if, as I hold, the 

 aeolian deposits of the Bahamas were formed with the sea at its 

 present level there would be a base-rock composed of coral-reef 

 debris; and it ought to be exposed during the retreating tide, where 

 cliffs front the sea. But a little reflection will show that situations 

 favouring its exposure would be usually inaccessible on account of 

 the breakers and the rollers ever dashing against the base of the 

 sea-cliffs. Such an examination would be hazardous in the Turks 

 Islands, for the sea is rarely sufficiently quiet on the weather coasts 

 of the islands where these sea-cliffs exist. In those places where 

 the cliffs lie a little inland, being cut off from the sea by the growth 

 of a fringing reef, extensive beaches with the sand piled up against 

 the foot of the cliffs would effectually prevent observation. The 

 most favourable localities would exist where a line of cliff washed by 

 the waves abuts on a beach. Even these do not always permit one's 

 approach ; but I found such an accessible spot in the Turks Islands, 

 and there was exposed, underlying the aeolian sandstone, a reef-rock 

 containing large fragments of corals. 



There are two points connected with these aeolian sandstones to 

 which A. Agassiz makes no allusion. The first is that this formation 

 seems to be peculiar to the Bahamian and Bermudian regions. 

 Calcareous sandstones, formed by the consolidation of wind-blown 

 sand derived from coral-reef beaches and composing entire islands, 

 are unknown in the great coral-reef regions of the Indian and Pacific 

 Oceans. The second point is concerned with the conditions under 

 which these aeolian rocks were formed. Their absence, more or less 

 complete, from other great coral-reef areas would seem to imply 

 that unusual conditions, mainly climatic, prevailed during their 

 formation in the Bahamas and in the Bermudas. Both these 

 matters are dealt with at the close of the chapter. 



The Author's Observations on the Geological Characters 

 of the Turks Islands. — The results are given here exactly in the 

 form in which they were written before the author had read the 

 memoir of A. Agassiz on the Bahamas. The remarks suggested by 

 the perusal of that work have since been intercalated. The sojourn 

 of the American naturalist in this group probably did not cover 

 more than a week or two ; but he seems to have visited all the islands, 

 including those that are most isolated, such as Eastern Cay and 

 Greater Sand Cay. Though few details are given by Agassiz, it will 

 be seen that the results obtained by the present writer are in general 

 agreement with his conclusion that the islands are formed in part of 

 aeolian sandstone and in part of shore coral-rock. However, the 

 distinction has to be made between the work of the past and of the 

 present in describing the formation of these islands. Whilst the 



