IV DEPTHS AND DEPOSITS OF THE OCEAN 169 



while in the lagoons of coral islands it may be found in a few 

 feet of water. Volcanic mud may be found extending into very 

 deep water — in fact, some of the deepest Red clays might be 

 called Volcanic muds, so abundant are the minute fragments of 

 pumice and volcanic glass — but in the neighbourhood of volcanic 

 islands the material from the land is generally masked by the 

 accumulation of pelagic shells, and the Volcanic mud may pass 

 into Pteropod ooze in depths of about 1000 fathoms, or into 

 Globigerina ooze in depths of 1500 or 2000 fathoms. Green 

 mud and Red mud generally occur in depths less than 1000 

 fathoms, the seaward limit being about 1300 or 1400 fathoms. 



Of the pelagic deposits, Pteropod ooze is found in shallower 

 water than any of the other types — from about 400 fathoms to 

 about 1500 fathoms, its seaward limit being reached in about 

 1700 or 1800 fathoms. Globigerina ooze may be found in all 

 depths from about 400 fathoms to over 3000 fathoms, but 

 occurs typically in depths between about 1200 and 2200 

 fathoms, its deeper limit in the Pacific and Indian Oceans 

 occurring at about 2800 or 2900 fathoms, while in the North 

 Atlantic it is known in depths approaching 3500 fathoms. 

 Diatom ooze occurs usually in depths of about 600 to over 

 2000 fathoms, but in the North Pacific it is found in depths of 

 4000 fathoms. Radiolarian ooze is a characteristically deep- 

 water deposit, hardly known in depths less than 2000 fathoms, 

 and covers the bottom at the greatest depths recorded by 

 the "Challenger" and "Nero" in 4500 to over 5000 fathoms. 

 Radiolarian ooze may, however, be regarded as a mere variety 

 of Red clay, containing a notable proportion of these siliceous 

 remains as a result of the favourable conditions in the surface 

 waters. Red clay is the typical deep-water deposit, and covers 

 wide areas in depths exceeding 2000 fathoms, occupying the 

 sea-floor in all the "deeps" except in one or two cases in the 

 North Atlantic, being displaced in certain parts of the Pacific 

 and Indian Ocean by its variety, Radiolarian ooze. 



The rate of deposition of materials on the sea-floor is Rate of 

 naturally beyond the range of direct measurement, at all events disposition. 

 in deep water. The only observations bearing on this point 

 have been recorded by Mr. Peake, who in 1903 on board the 

 S.S. "Faraday" raised and repaired a telegraph cable lying in 

 2300 fathoms in lat. 50^^ N. and long. 31° W. in the North 

 Atlantic. This same cable had been lifted from a depth of 

 2000 fathoms about 200 miles to the eastward in 1888 by 



