OF ARTS AND SCIENCES : MAY 26, 1868. 5 



500 fathoms) the decline of temperature from 79° (surface) to 41° 

 (334 fathoms) is thoroughly determined. So, then, low temperatures 

 have nothing to do with polar currents (which do not exist) or Gulf 

 Stream. 



Tempei*ature observations are wanted in the Gulf of Providence, 

 in this connection. 



II. A report, dated Key West, May 10, from Mr. L. F. 

 Pourtales, to the Supt. U. S. Coast Survey. 



You have no doubt heard from Mr. Mitchell of the results of our 

 cruise around the Salt Key Bank. In my line the results presented 

 nothing of very great or novel interest, except a few dredgings on ap- 

 proaching the Florida reef on our return. 



Since Mr. Mitchell's departure we have been engaged in running 

 lines of soundings from the reef to deep water, combined with dredg- 

 ings. At first we sounded and dredged on alternate- days, but by 

 working two lines, one on the drum and the other on the reel of the 

 donkey engine, we find no difficulty in sounding and dredging at the 

 same time, thus making the most of the fine weather with which we 

 have of late been favored. 



Thus far we have run four such lines and part of a fifth, and shall 

 run two or three more. The results are very interesting and pretty 

 accordant on the different lines. Beginning at the reef, the bottom ap- 

 pears to be composed of calcareous sand or mud, rather barren, un- 

 til we reach near the vicinity of the 100 fathoms' line, when the descent 

 becomes less rapid or almost ceases, indicating a rocky plateau, the 

 material of which is a highly fossiliferous recent limestone (in fact in 

 process of formation) in larger or smaller masses, or sometimes in 

 ledges on which the dredge is in great danger of being held fast. This 

 bottom is quite rich in animal life, particularly Terebratula, (my T. 

 cubensis very abundant, and another new species a little less so), 

 Cidaris, Comatula, and Annelids. Several species of corals occur also, 

 nearly all different from those found on the coast of Cuba, though of 

 the same or allied genera (Stylaster, 2 sp., Distichopora, Heliopora ? 

 and several forms of the family of Turbinolians). The Stylaster forms 

 sometimes considerable masses. But, as I find it nearer shore, the oc- 

 currence of corals appears to be very capricious ; you may get a dredge 

 full of one species in one place, and not find a trace of them in many 

 subsequent oasts in the same neighborhood. 



