42 



THE VOYAGE OF H.M.S. CFALLENGER. 



Fig. \9.—PorceUanaster cerideus, Wy. T. 



genera Glohigerina, Orhulina, Pulvimdina, Pullenia, and S-phceroklina — the two latter in 

 smaller pioportions. The ooze contains everyw^here, in addition to the foraminifera which 

 form its bulk, a quantity of mineral matter consisting of fragments of pumice, minute 



particles of felspar, particles and crystals of 

 other minerals due to the disintegration of 

 volcanic rocks, such as sanidine, augite, horn- 

 blende, quartz, leucite, and magnetite, and 

 rounded concretions of a mixture of the per- 

 oxides and protoxides of manganese and iron. 

 The globigerina ooze is essentially a calca- 

 reous deposit, so that it affords aljundaut 

 material for the calcareous shells and skeletons 

 of animals inhabiting the region where it is 

 being laid down. The foraminifera belonging 

 to the group of which the ooze is composed 

 live only on and near the surface, and are in 

 all cases dead when they reach the bottom, as 

 we have satisfied ourselves by the careful ol^ser- 

 vations of several years. They still contain, however, a quantity of organic matter in the 

 shell-chambers, and incorporated in the substance of the shell; and they, consequently, 

 afford sufficient food for many groups of abyssal animals which are nourished entirely by 

 passing the ooze through the alimentary tract. The globigerina ooze is accordingly a 

 deposit favourable to the support of animal life, and it is probably partly due to this 

 circumstance that the abyssal fauna appears to attain its maximum in the shallower 

 depths at which the ooze occurs. 



At depths greater than 2000 fathoms the carbonate of lime of the shells of Glo- 

 higerina is removed by the excess of carbondioxide in the sea-water ; the mineral matter 

 assumes a larger proportion in relation to the lime of the shells ; the ooze becomes gra- 

 dually darker, effervescing less freely with acid ; until at length it gives place to a more 

 or less homogeneous " red clay." The distribution of these two great formations may be 

 broadly defined thus : — The "globigerina ooze" covers the ridges and elevated plateaus 

 in the ocean, and generally occupies a belt at depths down to 2000 fathoms round the 

 shores, outside the belt of shore deposits ; and the " red clay " covers the floor of the 

 deeper depressions. An intermediate band of what we have called " grey ooze " occurs 

 at depths averaging perhaps from 2100 to 2300 fathoms. At one time I believed that 

 the red clay consisted almost entirely of the insoluble " ash " of the falling organisms 

 left after the whole of the calcic carbonate had been removed. My colleague, Mr Murray, 

 has studied very carefully the distribution of volcanic debris over the floor of the ocean, 

 and it is his opinion that the "red clay" is formed chiefly by the decomposition of 



