Chemical Composition of some Oceanic Deposits. 229 



2. ' Notes on the Chemical Composition of some Oceanic Deposits/ 

 By Prof. J. B. Harrison, M.A., F.G.S., and A. J. Jukes-Browne, 

 Esq., B.A., F.G.S. 



The authors formerly experienced great difficulty in comparing 

 their analyses of the Oceanic Deposits of Barbados with those of 

 modern oozes made by Dr. Brazier. Since then Dr. Murray has 

 placed samples of recent Red Clay and Globigerina-ooze at their 

 disposal, and these were analysed by Prof. Harrison and Mr. John 

 Williams. 



The results of analysis of the Eed Clay were arranged as follows : — 

 Argillaceous constituent 67'85 per cent., pumiceous matter 23*26 

 per cent., organic constituents 5-88, and adherent sea-salts 3*61 

 per cent. The authors found that the argillaceous constituent was 

 not a mixture of an orthosilicate of alumina and hydrated peroxide 

 of iron, having the proportion of silica to alumina as 14 to 12, 

 but a more highly silicated compound in which the proportions 

 were as 33 to 12. It was in fact a ferruginous earth, such as would 

 result from the decomposition of palagonite and of a basic volcanic 

 glass, fragments of which were frequent in the Pacific red clays. 

 The pumiceous matter was the debris of an acid pumice containing 

 7 per cent, of soda, and apparently therefore the pumice of a soda- 

 felsite. Comparing the analyses of the recent Bed Clay with those of 

 Barbadian red clays, they find the differences to be such as would 

 result from mixtures of the palagonitic earth with various acid and 

 basic pumices. A mixture of the palagonitic earth with the 

 pumiceous dust which fell on Barbados in 1812 would have a 

 composition closely corresponding to that of the Oceanic Clay of 

 Barbados. 



The recent calcareous ooze closely resembled the more calcareous 

 ' chalks ' of the Barbadian Oceanic Series, but the latter contained 

 much colloid silica and fine clay. The differences between the 

 analyses of the recent ooze and of English chalk, when certain 

 allowances are made, were found to be but small. The recent 

 calcareous ooze contained many more Globigerina-tests than Tertiary 

 or Mesozoic chalks, but it is suggested that this is due to our 

 possessing only the surface-layers of the Globigerina-ooze. 



In one important respect all the different kinds of deposit which 

 were examined resembled one another, namely, in the infinitesimally 

 small quantity of quartz which they contained. 



The authors' examination of the recent oceanic deposits, and 

 a comparison of them with the raised Barbadian deposits, only 

 increased their conviction that the latter were of truly oceanic 

 origin . 



March 20th.— Dr. Henry Woodward, F.R.S., President, 

 in the Chair. 

 The following communications were read : — 

 1. * On Fluvio-Glacial and Interglacial Deposits in Switzerland.' 

 By C. S. Du Biche Preller, M.A., Ph.D., F.G.S., F.C.S., A.M.I.C.E., 

 MJ.E.E. 



This paper is the outcome of one published in the ' Geological 



