of Edinburgh, Session 1876-77. 
247 
3. On the Distribution of Volcanic Debris over the Floor of 
the Ocean, — its Character, Source, and some of the Pro- 
ducts of its Disintegration and Decomposition. By John 
Murray, Esq. Communicated by Sir C. Wyville Thomson. 
Daring the present session I propose to lay before the Society 
several papers on subjects connected with the deposits which were 
found at the bottom of the oceans and seas visited by H.M.S. 
Challenger in the years 1872, 1873, 1874, 1875, and 1876. 
Instruments in use for obtaining information of the Deposits. 
It will be convenient to introduce this first communication with 
a brief description of the instruments and methods employed on 
board H.M.S. Challenger with the view of obtaining information 
and specimens of these ocean deposits. The instrument in most 
frequent use was the tube or cylinder forming part of the sounding 
apparatus. 
During the first six months of the cruise this cylinder was one 
having less than an inch bore, and was so arranged with respect to 
the weights or sinkers that it projected about six inches beneath 
them. The lower end of the cylinder was fitted with a common 
butterfly valve. This arrangement gave us a very small sample of 
the bottom. 
In July 1873 this small cylinder was replaced by one having a 
two-inch bore/ and it was also made to project fully eighteen inches 
below the weights. This was a great improvement, as it gave a 
much greater quantity of the bottom in most soundings. 
The tube was, in the clays, frequently forced nearly two feet into 
the bottom. On its return to the ship, the butterfly valves w'ere 
removed, and a roll of the clay or mud, sometimes eighteen inches 
in length, could be forced from it. In this way we learned that 
the deeper layers were very frequently different from those occupy- 
ing the surface. 
In the organic oozes— as the G-lobigerina, Pteropod, Radiolarian, 
and Diatom oozes — the tube did not usually penetrate the bottom 
over six or seven inches, these deposits offering more resistance than 
the clays and muds. Occasionally the tube came up without any- 
thing in it, but the outside was marked with streaks of the black 
