198 THE ATLANTIC. [cH vp. 11 
in a vertical direction twenty-five times; so that while 1 mm. 
represents 10 miles in distance, 2°5 mm. represent one mile or 
1000 fathoms in depth or height. 
A reference to this section shows that the bottom of the 
Atlantic, along a line which corresponds roughly with the 
Tropic of Cancer, presents very much the same character which 
it does farther north—that of a plateau showing comparatively 
gentle undulations on a large scale. The section does not dif- 
fer very materially from the general outline given in some of 
the latest atlases of physical geography—for example, in Plate 
XLI*' of Stieler’s Hand Atlas; and it confirms, upon the whole, 
to a remarkable degree, the soundings of Lieutenant-command- 
ing Lee and Lieutenant-commanding Berryman, of the United 
States Navy, in the surveying-ship Dolphin, which have fur- 
nished nearly all the data for this particular region. 
After passing over about 80 miles of volcanic mud and sand, 
products of the disintegration of the volcanic rocks of the isl- 
ands of the Canary group, the first four soundings, to a distance 
of 300 miles from Santa Cruz at depths varying from 1525 to 
2220 fathoms, yielded “ globigerina ooze” of the usual charac- 
ter. This “modern chalk” consists, first of all, of a creamy 
surface layer made up of little else than the shells, most of 
them almost entire, of Globigerina, Pulvinulina, and Orbulina, 
with a relatively small proportion of finely divided matter, con- 
sisting chiefly of coccoliths and rhabdoliths, and a still smaller 
proportion of the spines and tests of radiolarians, and frag- 
ments of the spicules of sponges. Mixed with these there are 
usually a considerable number of the dead shells of pteropods 
of the genera Cleodora, Diacria, Cavolinia, Triptera, and Styli- 
ola in a more or less mutilated and disintegrated condition ; 
and living among the ooze, at all events at moderate depths, 
there are scattered examples of many foraminifera of the cris- 
tellarian and milioline groups, and the sponges, corals, star- 
fishes, and higher invertebrates, which, with a few fishes be- 
