326 PROF. HARRISON AND MR. JUKES-BROWNE ON [Aug. 1 895, 



this similarity being even more apparent when the adherent sea- 

 salts are removed ; the ' Challenger ' sample then has 93 - 46 per 

 cent, of calcium carbonate, and the ' Buccaneer ' sample has just 

 92 per cent. The amounts of iron and manganese oxides are prac- 

 tically the same in both, and those of combined silica differ but 

 little. The adherent sea-salts amount to 2-48 per cent, in the one, 

 and 2*70 per cent, in the other. 



Y. Comparison with Tertiary and Cretaceous Chalk. 



None of the Tertiary chalks of Barbados which we examined 

 contained as much as 90 per cent, of calcium carbonate, because 

 they are associated with radiolarian earths, and most of them 

 include from 10 to 20 per cent, of siliceous organisms, and from 9 

 to 13 per cent, of clay. Several of them, however, contain about 

 80 per cent, of calcium carbonate, and these compare very well 

 with the ' Challenger ' sample A, so far as chemical composition is 

 concerned — especially when the adherent sea-salts of the latter are 

 subtracted, and the other ingredients are re-calculated to a percentage. 

 This has been done, and the result tabulated under column A, 

 beside which are placed the analyses of two Barbadian chalks taken 

 from our former paper in this Journal, vol. xlviii. (1892) p. 185 : — 



'Challenger.' CaneMcL Cleland . 

 A. 



Loss on ignition 1-90 2*59 184 



Calcium carbonate 83-61 83-23 79-84 



Calcium phosphate '25 '35 "38 



Colloid silica : 4-05 5-02 7'36 



Quartz -17 -05 01 



Silicates, iron, etc 8'96 6"28 965 



Manganese peroxide '36 l - 43 '91 



Alkalies -65 '37 -01 



99-95 9932 lOO'OO 



The other two oozes have an exceptionally large proportion of 

 calcium carbonate, and are not therefore comparable with Barbadian 

 chalks. These chalks have a greater resemblance to the oozes 

 which contain between 60 and 80 per cent, of calcium carbonate, 

 but we have not analysed any of these, and Dr. Brazier's analyses 

 do not afford a sufficiently accurate basis of comparison. Attention, 

 however, may be directed to the infinitesimal amounts of quartz 

 which both oozes and chalks contain, the amount in the oozes 

 ranging from -04 to '55, and in the chalks from *01 to "69. 



With regard to Cretaceous chalk, few analyses have been made 

 with that amount of care which is necessary for a proper comparison 

 with our analyses of recent ooze. We decided, therefore, to have 

 several samples of Middle Chalk analysed by the same methods. 

 These analyses were carried out at Georgetown in the Government 

 Laboratory under the supervision of one of us, and with the assist- 

 ance of Mr. J. Williams. The results are as follows : — 



