172 MIXEBALS IN COBAL-LIMESTONES OF BABBADOS. [vol. Lxxv,. 



Hills, 1 of the Devonian Limestones of South Devon, 2 and of the 

 \Veniock Limestones, 3 as well as the searching enquiry by Joseph 

 Lomas into the inorganic constituents of the Crag. 4 These earlier 

 studies dealt mainly with limestones containing relatively high 

 proportions of extraneous constituents, but were not quantitative ; 

 the present one indicates that, even where the extraneous con- 

 stituents are present in relatively small amounts, the enquiry can 

 be readily made a quantitative one in determining the various 

 minerals present in minute amounts. 



The Presence of Titanium Oxide in the 

 Mineral Residua. 



In the analyses quoted in these notes titanium oxide is invariably 

 shown. In the course of the earlier work done by Jukes-Browne 

 and myself on the ' Composition of some Oceanic Deposits,' I did 

 not determine the titanium oxide in the samples examined, our 

 main object being a comparison of the Miocene oceanic deposits 

 of Barbados with recent oozes obtained during the Challenger 

 Expedition. Hence in analyses quoted in them, as in the Chal- 

 lenger Report on Deep-Sea Deposits, the titanium oxide was not 

 separated from the alumina. 



I have recently determined the proportions of titanium oxide in 

 the samples of Barbados Oceanic Clav and of deep-sea dredgings 

 (all dried at 110° C.) to be as follows :— 



Barbados Oceanic Deposits. 



Deposits in descending TiO? I Stations, Challenger Ti0 2 



order. per cent. I Dredgings. per cent.. 



1. Volcanic mudstone (highest | 186 Atlantic Red Clay, 2740 f.... T92 



stratum). Oceanic deposits. 2-85 | 256 Pacific Bed Clay, 2960 f. ... 2*01 



2. Creamy white Oceanic Clay ... 2-92 j 2 24 Do. G Jobigerina Ooze, 



3. Creamy yellow do. ...3-63 1850 f '08 



i. Mottled pink and vellow Ocea- i 238 South Atlantic Globigerina 



nic Clay 330 Ooze, 1990 f. 'II 



5. Bright red Oceanic Clay 3*59 I Buccaneer Expedition, 1885, 



6. Dark chocolate-red Oceanic South Atlantic Globi- 



£i a y 5.-3 gerina Ooze, 1815 fathoms. *23 



It is evident that the deep-sea claj^s forming the highest beds in 

 the Barbados Oceanic Series were derived from volcanic debris, 

 of lavas such as pyroxene-andesite or basalt, containing rela- 

 tively high proportions of ilmenite or of a titaniferous magnetite. 

 On the other hand, the volcanic debris in the lower ash-beds of the 

 series are mainly persilicic and pumiceous, and hence derived from 

 rlrvolitic or trachytic magmas. 



1 Q. J. G. S. vol. xlvii (1891) p. 550. a Ibid. vol. xlviii (1892) p. 377. 



3 Ibid. vol. xlix (1893) p. 236. 4 Ibid. vol. lvi (1900) p. 738. 



