314 PROF. HARBISON AND MR. JUKES-BROWNE ON [Aug. 1 89 5, 



oozes the errors would approach those discoverable in the analyses 

 of the ' red clays.' 



The analyses which follow were made by one of us in the Govern- 

 ment Laboratory of British Guiana, with the collaboration of Mr. 

 John Williams, F.C.S., the Assistant Government Chemist. The results 

 have been considered by both of us, and the paper has been finally 

 written out by the author resident in England. In order to secure 

 really useful and accurate results much tedious laboratory work is 

 required, and moreover each analysis has been checked by repetition. 

 In this work, and also in the arrangement of the results, Mr. J. Wil- 

 liams has afforded us very considerable assistance, for which our 

 thanks are due to him. 



Some detailed analyses of English Chalks have also been made in 

 the same way, for comparison with those of the Barbadian Chalks 

 and the recent Globigerina-oozes. 



We propose to deal first with the ' red clay,' comparing it with the 

 coloured earth of Barbados, and thereafter to discuss the calcareous 

 oozes and their more ancient prototypes. 



II. Analysis of Bed Clay. 



This material was a red clay obtained from Station 256 in the 

 Pacific, lat. 30° 22' N. and long. 154° 56' W., at a depth of 2950 

 fathoms. Our sample was analysed in the way usually employed for 

 clays, but the soluble silica present was determined in the manner 

 described in our paper on the Oceanic Deposits of Barbados. 1 The 

 alkalies were separately determined. The material was also tested 

 for the existence of crystalline quartz by the method indicated in 

 that paper, and as the amount found was only just appreciable ( - 01 

 per cent.), the silica in the siliceous residue left after boiling with 

 sulphuric acid and fusing with microcosmic salt is entirely combined 

 silica. 



But even when we have separated the quartz and colloid silica, 

 we do not gain much information by merely setting down the 

 amounts of silica, alumina, etc. in the residue. In these deep-sea 

 clays some of the material is evidently a clay in a state of very fine 

 division, but the high percentage of silica shown by ordinary analysis 

 is sufficient to indicate the presence of some other substance. 



[Having reason to believe that this substance was disintegrated 

 pumice, we separated it in the following way : — A portion of the clay 

 was boiled repeatedly with strong sulphuric acid (about 94 parts 

 H 2 S0 4 and 6 of water), which has the power of decomposing clay and 

 the decomposition-products of volcanic rocks, but is practically with- 

 out action on a glassy pumice. The residue from this treatment 

 was then digested with hydrochloric acid, in order to dissolve out any 

 basic sulphates which might have been formed ; and the remaining 

 insoluble residue was boiled with a solution of caustic potash, in 

 order to remove the soluble silica set free by the acid treatment. This 

 process is, in fact, the same as that used by Dittmar in his prepara- 



1 Quart. Journ Geol. Soc. vol. xlviii. (1892) p. 183. 



