A TRIP TO TRINIDAD. 



383 



above the sea is usually nothing more than a species 

 of marble, or a collection of fragments of madrepore, 

 cemented by carbonate of lime, with broken shells 

 and sand. It is important to examine, in each cay, 

 upon what this class of rock rests ; if it rises from 

 works of still living mollusca, or from those second- 

 ary and tertiary rocks, which, from the appearance 

 and preservation of the coral remains they contain, 

 might be supposed to be modern productions. The 

 gypsum of the cays off San Juan de los Eemedios, 

 on the northern coast of Cuba, is worthy of great 

 attention; for its epoch surely ascends beyond the 

 era of history, and no geognostic observe? will deem 

 it to be the product of the mollusca of our seas. 



It was from Cay de Piedras that we first saw, 

 toward the east-northeast, the high mountains that 

 rise back of the bay of Jagua. We again passed 

 the night at anchor, and on the following morning, 

 the 12th of March, running out between the north 

 point of Cay de Piedras and the coast of Cuba, we 

 entered upon the clear and open sea. Its deep blue 

 color, and increased temperature, proved to us the 

 much greater depth of the water. The thermometer, 

 which, in soundings of six and a half, and eight feet 

 of water, we had often found at 22°.6 C. (72°.7 F.), 

 now rose to 26°.2 C. (79° F.), while during these 

 observations it stood in the air at from 25° to 27° C. 

 (77° to 80°.6 F.). Availing ourselves of the varia- 



