ITS COMPOSITION AND CAUSE. 63 



of the sea. A black petrel, (Procellaria fu- 

 liginosa,) in this latter condition, was taken by 

 our boat's crew and brought to the ship. It was 

 sufficiently lively when on board ; and the state 

 in which it was found could scarcely be at- 

 tributed to repletion, for, on dissection, I found 

 its stomach perfectly empty. Janthinae, or sea- 

 snails, were the most abundant of the floating 

 rnollusks. Their number was immense ; and 

 their floats contributed greatly to the white, 

 appearance of the froth-line. One species of 

 this family, which I obtained here, was new to 

 me ; and is certainly very rare : its shell was 

 yellow ; rather smaller and more elongated than 

 J. communis ; and the whirl more prominent 

 and spiral. The contained animal was also of a 

 yellow colour ; but in the form of its float, and 

 other respects, it closely resembled the ordinary 

 blue-shelled species. 



This line of miscellanies on the ocean, denoted 

 the termination of a current,* which, in its 



* Immediately after passing this spot, we lost the strong 

 N. W. current that had hitherto accompanied us ; and it 

 is worthy of remark, as associated with the limits of 

 currents, (which are often capricious,) that some of our 

 older navigators have recorded the existence of a current- 

 ripple, and others that of a froth, in nearly this precise 

 place. 



