328 THE CHEMICAL COMPOSITION OF OCEANIC DEPOSITS. [Aug. 1895, 



thick-shelled, but are not so closely packed as in B and C ; there 

 is, moreover, a larger number of immature specimens. Mr. Hill 

 reports that ' the matrix consists largely of calcareous particles 

 derived from the Globigerince, but there is a certain admixture 

 of minute siliceous particles and of sponge-spicules ; a few entire 

 radiolaria can also be seen, and I should have thought that there was 

 more than 4 per cent, of such siliceous material. There is also a 

 certain amount of very fine siliceous matter, which gives the matrix 

 a peculiar translucent appearance similar to that which is seen in a 

 section of marl or clay. This is probably hydrated silicate of 

 alumina, and there is in one place a definite film, strong enough to 

 carry part of the test of a Globigerina in section, and by polarized 

 light separate calcareous atoms seem to float in the film, while the 

 carrying material is extinguished on rotation.' 



Dr. John Murray informs us that these are typical examples of 

 the more calcareous oozes, and that deposits of a chalky character 

 were not common among the ' Challenger ' di'edgings. It occurs to 

 us that this may be due to the surface-character of the dredgings ; 

 the upper layers of the Globigerina-ooze must be full of the tests of 

 recently dead foraminifera, but these tests have not had time to 

 undergo alteration and disintegration. In the lower layers, which 

 have been for a long time exposed to the chemical action of the sea- 

 water, it seems likely that some alteration would take place. 

 Probably many of the tests fall to pieces, thereby increasing the 

 proportion of finely-divided material, and a certain amount of com- 

 pression must also occur. If this view be correct, the resulting 

 material would have as close a similarity to Chalk in structure as 

 the surface-ooze has in chemical composition. 



In conclusion we may remark that our examination of these 

 recent deep-sea deposits, and a comparison of them with the raised 

 Barbadian deposits, have only increased our conviction that the 

 latter are truly of oceanic origin. 



Discussion. 



Mr. W. W. "Watts congratulated the Authors on having been able 

 to derive their information with regard to the Bed Clay from actual 

 specimens, while descriptions were all that were at present accessible 

 to others. He wished to enquire by what means the pumiceous con- 

 stituents had been separately estimated, and whether the manganese 

 nodules had been excluded from the analysis of the Bed Clay. 

 , Dr. W. F. Hume said that the West Indian deep-sea deposits display 

 the nearest resemblance of any to the Cretaceous deposits. Dr. Murray 

 had already shown the great resemblance of certain marls in this 

 region to the Chalk Marl, and now the Authors had shown that the 

 Globigerina-oozes differ but little from those of the Turonian Chalk 

 of England. As the West Indian region is one of the principal 

 areas where assemblages of arenaceous foraminifera occur specifically 

 identical with those of the Chalk Marl, the interest of these 

 comparisons becomes considerably increased. 



Dr. G. J. Hinde, Mr. Clement Beid, and Mr. J. E. Make also 

 spoke. 



