100 PRESIDENT S ADDEESS. 



carefully examined the composition of the material from a dredg- 

 ing of 1,862 fathoms in this district, and, after cleaning away 

 the finest mud, found that of the residue Bilooulina ringens 

 formed fifty per cent., the arenaceous Haplophragmium subglolo- 

 sum, M. Sars, twenty per cent., but Globigerinse only four per 

 cent. A calcareous deposit is thus taking place in the Arctic 

 Seas, the component constituents of which appear to differ ma- 

 terially from the Globigerina Ooze of other parts of the ocean. 



{c) Red and Gray Clays. — These clays are being laid down 

 over vast districts in the Pacific, Southern, and Atlantic Oceans, 

 at depths which exceed 2,000 fathoms. In the great abysses of 

 the ocean the water possesses a solvent power, and takes back all 

 the carbonate of lime which, under other conditions, the animals 

 had themselves borrowed from it, and with which they had com- 

 posed their shelly coverings or bony skeletons. It has been 

 suggested that the dissolving character of the water arises from 

 excess of carbon-dioxide, but the exact depth at which it begins 

 to act appears to be from some unknown cause a fluctuating one. 

 Few lime-secreting animals live in this mud, and the shells of 

 Oceanic MoUusca and Foraminifera are dissolved as they fall 

 through the three or four miles of water, or soon after reaching 

 the bottom. Here, then, we no longer have a Griobigerina Ooze 

 but gray, red, or dark chocolate-coloured mud. "The red and 

 chocolate colours of many of these clays is due to the presence of 

 oxide of iron in the first and oxide of manganese in the latter in- 

 stance." (Murray.) The origin of this mud has been a source of 

 several theories, the one which at present finds most favour is 

 that of Mr. Murray, who holds that it depends chiefly on volcanic 

 matter, consisting of the felspar, of pumice, and scoria, together 

 with the minerals incorporated with them. He supposes that 

 the pumice, after floating for some time upon the surface, gradu- 

 ally "weathers" away, and the particles sink to the bottom. 

 Manganese is being deposited in large quantities at these depths ; 

 it accumulates around some nucleus, which may be the ear-bone 

 of a whale, or a shark's tooth, a small mineral, or piece of bone, 

 and often forms large masses. Sometimes the trawl of the 

 ' Challenger'' would bring up as much as a bushel of manganese 



