24 NATURAL SCIENCE. march. 



30 per cent, of the deposit. They have been found also in the Central 

 Indian Ocean, and in other deposits besides the red clay. They occur 

 as extremely minute prisms, crossed twins, and as globular or 

 spherulitic aggregates. There appears to be a connection between 

 the distribution of phillipsite and that of the fragments of basic 

 volcanic glass and basaltic lapilli. This leads the authors to conclude 

 that the materials of the former have been derived from the latter ; 

 so that there is in this case no violation of the law connecting the 

 formation of zeolites with the decomposition of igneous rocks in their 

 immediate neighbourhood. 



We have now to refer briefly to that portion of the report which 

 deals with the nature and distribution of the different deposits. Red 

 clay is found in the greatest depths and at the greatest distance from 

 land. It is the most widely distributed of all the deep-sea deposits, 

 and was found at seventy stations which range in depth from 2,225 

 to 3,950 fathoms. The colour and amount of hydrated silicate of 

 alumina are both liable to considerable variation. In the North 

 Atlantic the colour is a brick-red, owing to the presence of a thin pellicle 

 of ferric oxide on the surfaces of the minute mineral particles. In the 

 South Pacific and Indian Oceans, the deposit often assumes a 

 chocolate-brown colour, in consequence of the presence of minute 

 rounded grains of peroxide of manganese. Unlike a pure clay, this 

 deposit will fuse in the blow-pipe flame to a black, often magnetic 

 bead. As a rule, the red clay is smooth and soapy to the touch, but 

 occasionally a gritty feeling, due to the presence of pellets of peroxide 

 of manganese, zeolitic crystals, or fragments of pumice, may be 

 noticed. The extraordinary abundance of manganese nodules, 

 sharks' teeth and cetacean ear-bones has already been mentioned. 

 Hydrated silicate of alumina never forms more than one-half of the 

 deposit. Carbonate of lime ranges from i or 2 per cent, in the deeper 

 parts to 20 per cent, near the upper limit. It is due to the presence 

 of the remains of calcareous organisms which resemble those living 

 at the surface in the same neighbourhood. Large and small frag- 

 ments of pumice were dredged and trawled in great numbers and in 

 almost all regions. The mineral constituents are those of volcanic 

 rocks — sanidine, plagioclase, augite, hornblende and magnetite. 

 Ice-borne fragments of rock and terrigenous minerals are found in the 

 Southern Ocean. 



Radiolarian ooze, like the red clay, is found only in the greatest 

 depths. The constituents are the same as those of the preceding 

 deposits, but the relative proportions are different. The remains of 

 radiolaria and siliceous organisms make up at least 20 per cent. — in 

 one case 80 per cent. — of the deposit. The nine specimens obtained 

 by the " Challenger " range in depth from 2,350 to 4,475 fathoms. 

 Radiolarian ooze is known only in the Pacific and Indian Oceans. 

 It has not been found in the Atlantic. 



Diatom ooze is mainly composed of tlie frustules of diatoms, but 



