SUBMARINE DEPOSITS. 283 
jurassic period have gradually filled the shallow sea formerly 
existing to the west of the Mississippi basin and of the southern 
portion of the Gulf States. In more recent times, the muds 
brought down by the Mississippi and other rivers emptying into 
the Gulf of Mexico have been deposited upon its shores, and 
have formed the steep continental slope of the Gulf beyond the 
hundred-fathom line. 
The recent river muds now occupy a narrow strip of the Mis- 
sissippi basin, between Louisiana and Mississippi, as far north as 
the mouth of the Ohio. "They have also built out the delta of 
the river to within a short distance of the hundred-fathom line, 
and extend along the shore of Texas, slowly filling up 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 immense number of dead pteropod and hetero- 
pod shells which it contained, in addition to the countless tests 
of globigerinz and orbulinz. These shells belonged mainly to 
the genera Clio, Hyalea, Triptera, Atlanta, Styliola, ete., all of 
which swarm on the surface, or a little below 3t, in all the parts 
of the Guif of Mexico which we had thus far passed over. 1 
could at once see how important a part these dead pteropod shells 
must play in the formation of the sedimentary matter accumulat- 
ing at the bottom.  Globigerinze and orbuline 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 is the rule in all specimens of the bottom which I have 
thus far had time to examine. The decay and solution of the 
test become more rapid with increasing depth, and may be due, 
as suggested by Mr. Murray, to the excess of carbonic acid 
present at great depths, or, as Professor Dittmar is inclined to 
believe, to the solvent aetion of the sea-water itself. In a vol- 
canic region like that of the West Indies, there is no difficulty 
in accounting for the presence of a large supply of gas. To 
show how far the dead pteropod shells make up the globigerina 
