4 THREE CRUISES OF THE BLAKE." 
the ocean is played by the pelagic forms which, after death, 
slowly find their way to the bottom and form at the pre- 
sent day deposits in every way similar to those of the chalk. 
Mr. Murray has, however, from the more extended explorations 
of the “Challenger,” clearly proved that the deposits going on 
beyond the continental platforms, at great depths in the oceanic 
basins, find no analogue among the stratified rocks with which 
we are acquainted. Professor Agassiz and Sir Wyville Thom- 
son also soon became convinced, as a result of their experience 
in deep-sea explorations, that the oceanic basins were of great 
antiquity and have always existed, and that the animals found 
at great depths existed under conditions which have remained 
unchanged from a remote period of time. 
Sir William Thomson, who became interested in deep-sea 
soundings from his connection with the laying of submarine 
Fig. 2. — Sir William Thomson's Sounding Machine. (Thomson.) 
cables, made a trial in 1872 of a machine he had devised 
for sounding with a piano-wire line. This machine (Fig. 
2), and his first use of it in sounding, is thus described by 
him : “I sounded from the ‘Lalla Rookh, with a lead weight 
of thirty pounds, hung by nineteen fathoms of cod-line from 
another lead weight of four pounds, attached to one end of a 
three-mile coil, made up of ends of piano-wire spliced together 
and wound on a light wheel about a fathom in circumference, 
made of tinned-iron plate. The weight was allowed to run 
directly from the sounding-wheel into the sea, and a resist- 
ance exceeding the weight in water of the length of the wire 
