lS4G.] Temperature of the Waters of the Gulf Stream. 211 



attention to the geological features of many of the islands of the 

 West India group. They appear for the most part, to owe their 

 origin to volcanic agencies, with the exception of much of their 

 lower portions, particularly those situated immediately along the 

 sea coast; these are chiefly composed of travertin, or recent lime- 

 stones. This limestone is of a light yellowish color, some parts 

 of it being very compact, while a great proportion exhibits a 

 concretionary or pisolitic structure, embracing recent corals, and 

 comminuted shells in great abundance, which still have an ex- 

 istence in the neighboring sea. 



This limestone has unquestionably been derived from thermal 

 springs, which always abound in volcanic regions, and generally 

 contain very considerable quantities of lime in suspension among 

 their waters: many of these are well known to have an existence 

 beneath the oceanic waves of this district, having been recorded 

 by numerous voyagers, from times far remote, whose duties have 

 hitherto led them to navigate these seas. But the most convincing 

 proof is in the structure of these pisolitic concretions: they are of 

 a spherical form, and of the size of a pea, and sometimes larger, 

 being composed of concentric lamina, arranged around a particle 

 of sand as a nucleus. Whenever one of these springs forces its 

 upward way through a sandy bott'om, a large number of these 

 particles are disturbed, and set in motion by the rapid ebullition 

 of the water, and are there kept .continually revolving, until they 

 become completely coated by these concentric lamina of lime, 

 and at length having obtained a sufficient weight, they again fall 

 by their own gravity; here a deposition of the lime having taken 

 place, and continuing to do so until the concretions are firmly 

 united in one solid mass, collecting the fragmentary corals, and 

 shells, that lie strewed along the bottom wherever the springs 

 occur. In the course of time, by the uplifting of these islands, 

 this newly formed limestone is brought to the light of day, and 

 disclose to view the appearance which they every where at pre- 

 sent exhibit. It is to the numerous thermal springs in this por- 

 tion of the globe, that I consider the elevated temperature of the 

 water of the gulf stream, principally to owe its origin. 



