668 PROCEEDINGS OF SECTION E. 
earliest knowledge that we have does not extend back further 
than fifty years; but it was not till the ‘‘Challenger” expedition, 
only twenty years ago, that any thorough and extended accumula- 
tion of facts was made. Since then we have had the soundings in 
the North Pacific by the ‘‘ Tuscarora” and the ‘‘ Enterprise” (both 
American). And in the Atlantic and Indian seas, moreover, we 
have had numerous sectional soundings of the ocean bottom made 
in connection with the multitude of submarine cables, which have 
greatly added to the knowledge of the subject. But for fullness of 
detail in every particular that demonstrates the nature and physical 
character of the ocean at every depth, and the form and com- 
position of the bed of the ocean, nothing has approached the results 
obtained by the scientific staff of the “Challenger,” which have 
now been completely published in some fifty bulky quarto volumes. 
As these are rarely accessible, I have availed myself of them, 
and particularly the last two volumes, which contain the masterly 
summary of my friend Dr. John Murray, who took up the work 
after the lamented death of Sir Wyville Thomson. 
Yet, after all, our knowledge of the subject is still very slight 
and only provisional, seeing that the observations have been 
limited to irregular lines very sparsely distributed over the ocean 
according to the tracks of the exploring ships. Even a few miles 
north or south of their course, great features may exist which 
escaped notice. 
The observations made at the different stations or points 
of deep water were, Ist, the depth; 2nd, the temperature at 
frequent intervals from the surface to the sea bottom, and also 
the chemical composition and specific gravity of the sea at all 
depths ; 3rd, the nature of the material which formed the deposit 
at the bottom ; 4th, the determination of the nature of the animal 
and vegetable life at every depth and at every distance from the 
nearest shore land. 
The result of the investigation goes to show— 
1. That surrounding all continents and the satellite islands a 
wide fringe or shelf has been formed by the spreading out of the 
detritus, resulting from the atmospheric denudation of the land 
and the erosion of the shore line by the sea waves. The coarse 
detritus, including the finest sand, rarely extends to 500 fathoms 
or half a mile indepth. The mean slope of the shore or terrigenous 
deposits is about 1 in 40, or about our steepest railway grade. 
There are exceptionally steep grades in some cases which are most 
probably due to the shelving shore formation having been eaten 
into by deep ocean currents, as for instance, west of Europe, 
when the shelf contour continues as a flat plateau, the depth of 
the water being only 600 feet 200 miles west of Lands End ; it 
then descends with a slope of 1 in 12 to a depth of 12,000 feet, 
which is about the average depth of the great flat bottom of the 
