6 BULLETIN OF THE 



Gulf of Mexico at similar depths. This is the more important because 

 the hydrography of the gulf is now, as you well know, so far advanced 

 that when the present season is finished, and the results are plotted, 

 we shall have a hydrographic chart with accompanying temperature 

 profiles in sufficient number to give an admirable account of the Physi- 

 cal Geography of the Gulf of Mexico, 



I was very much struck, on first seeing the ooze of the deep water of 

 the Straits of Florida between Havana and Florida Keys, with the im- 

 mense number of dead Pteropod shells which it contained, in addition to 

 the countless tests of Globigerinse and Orbiculina). These shells belonged 

 mainly to the genera Clio, Hyalsea, Triptera, Atlanta, Styliola, etc., all of 

 which swarm on the surface, or a little below it, in all the parts of the 

 Gulf of Mexico which we have thus far passed over. I could at once see 

 how important a part these dead shells of Pteropods would play in the 

 formation of the sedimentary matter accumulating at the bottom. Globi- 

 gcrina) and Orbiculina) form, as we know, the bulk of the ooze, but the 

 remaining part of the mud is made up mainly of the dead shells of 

 Pteropods in all stages of disintegration, from perfect shells, still filled 

 with the decaying animals, to the most minute grains, in which we can 

 just detect the presence of the Pteropod test. This composition of the 

 ooze was the universal rule in all specimens of the bottom which I have 

 had thus far time to examine. This plainly shows that Pteropods as well 

 as GlobigerinsQ and Orbiculinte, with other pelasgic animals swarming at 

 the surface of the sea at great distances from the land, are an important 

 fixctor in the composition of all the deep-sea deposits going on at the pres- 

 ent day. Of course they must have played a similar part in the deposition 

 of amorphous limestone formations in former geological periods. Whether 

 this decomposition of the test becomes more rapid with increasing depth, 

 as is the case in the deep-sea red clay of the "Challenger," I have not yet 

 been able to ascertain, from the rapid examination of the samples of 

 bottom thus far obtained. To show how far the dead Pteropod shells 

 make up the Globigerina ooze, I took, from the contents of the trawl 

 from 8G0 fathoms, equal portions of mud as it came up ; one part was 

 left and roughly measured, the other was first carefully sifted, the Ptero- 

 pod shells and their fragments were then collected, and likewise meas- 

 ured, when their bulk was foimd to bo somewhat more than half the 

 bulk of the sifted mud from which they came. This mud was intensely 

 cold, and it was a strange sensation to have your back and head burn- 

 ing under the scorching rays of the sun, while handling, with benumbed 

 fingers, the icc-culd masses of mud of 31)^° Fahrenheit, brought up by 

 the dred^'c. 



