10 
THE VOYAGE OF H.M.S. CHALLENGER. 
waa frequently attached to the beam of the trawl and iron frame of the dredge, and 
gave in most cases information of the immediate surface-layers of the bottom that could 
not be obtained by the trawl, dredge, or sounding tube. A tow-net was in like manner 
Pio. 15. — Onliaarj method of using the Tow-Net. 
sometimes fixed to the weights that were placed on the trawling line, some 200 to 500 
fathoms’ in front of the dredge or trawl. This net occasionally came up filled with mud 
or ooze. 
In another way, however, the surface-nets gave still more valuable information. 
During almost every day of the cruise these nets were dragged at the surface and in 
depths of 10, 20, 50, and 100 fathoms,* either from the ship or from small boats lowered 
for the purpose. Occasionally they were sent down to and dragged at depths of 500, 
1000, and 1500 fathoms.’ The contents of the deeper nets were carefully compared with 
the contents of those dragged at the surface and in shallow water. Again, the organic 
remains found in the deposits at the bottom were carefully compared with the animals 
captured in the tow-nets on the same day or in the same region. Hundreds of observa- 
tions of this kind, repeated day after day, led to a very accurate conception of the part 
played by surface organisms in determining the nature of the deposits now forming on 
the floor of the ocean at different depths and in different latitudes throughout all parts 
of the world. 
(Jn every occasion during the cruise when the anchor was heaved on board, it was 
carefully inspected, and specimens of the mud which came up on it were examined and 
pre8cr\'c<l. Recently Mr. Buchanan anchored one of the telegraph ships in 1600 fathoms^ 
with an anchor specially arranged to bring up a specimen of the deposit (see Fig. 16). 
This was a Tropman anchor, weighing 5 cwts.,’ the flukes being connected by a 
frame to which a canvas bag was laced ; with this he obtained over 1 cwt.® of 
Globigcrina Ooze. 
Tlie various contrivances have now been indicated by which information is obtained 
concerning the de{) 08 its now forming on the floor of the great oceans and inclosed seas. 
Although there are many mcKlifications in the trawls and dredges not here referred to, 
these are not of any essential importance as regards the information furnished about the 
’ 368 tn 914 tr.elrc^. * 18'3, .'J6'0, 91 '5, and 183 metres. ® 914, 1828, and 2742 metres. 
* S936 metr«t. * 253‘7 kilogrammes. ® 60"7 kilogrammes. 
