1918 J Davis: The Radiolarian Cherts of the Franciscan Group 307 



earths of the upper member of the oceanic deposits of Barbados. 

 There are certain points of difference — for example, the modern Red 

 Clay contains less alumina and more iron than the Barbados earths — 

 but such variations are to be expected in a material like the Red Clay 

 and, as a result of their chemical work, Harrison and Jukes-Brown 

 were convinced that this earth is the equivalent of the modern Red 

 Clay. 



It is believed that the oceanic deposits originated in deep water, 

 because of the general character of the deposits, and the practical 

 absence of larger organisms than radiolaria and foraminifera. The 

 chemical work above cited points to a deep sea origin for the upper 

 member and the siliceous earths are exactly what one would expect 

 the modern radiolarian oozes to become. Also the Oceanic Series 

 contains a species of echinoderm which has never been found at depths 

 less than 1000 fathoms. 



The succession of beds in Barbados is interpreted to mean that 

 the region sank beneath the ocean, beyond the reach of terrigenous 

 sediments, and continued to sink gradually until it reached depths 

 comparable with those under which radiolarian oozes are now accumu- 

 lating (2000-3000 fathoms). After a long period of abyssal condi- 

 tions there was a reversal and a reelevation of the region into depths 

 at which calcareous oozes could accumulate, after which the region 

 sank again and red clay was deposited. 



The only objection ever made to this interpretation of the Bar- 

 bados earths as abyssal deposits was made by Rust. 42 He states that 

 the radiolaria found in the Barbados earth are of types which, accord- 

 ing to the ' ' Challenger ' ' report, are dwellers in the deep sea, but 

 that the large admixture of foraminifera and other shells make it 

 doubtful whether these rocks are really abyssal. 



In Trinidad, 43 there is a succession of oceanic deposits quite sim- 

 ilar to those in Barbados. These oceanic deposits are called the 

 Naparima marls and are believed to be Miocene. They rest uncon- 

 formably with gentle dips upon an older series of red and blue clays 

 and sandstones. In this series, as, in Barbados, there is a continuous 

 gradation from a basal member, consisting of buff to cream colored 



« Rust, Beitrage zur Kenntniss der fossilen Radiolarien aus Gesteinen der 

 Trias und der palaeozoischen Sehichten. Palaeontographka, xxxvni, 121, 

 1 891-92. 



43 Harrison and Jukes-Brown, The Oceanic Deposits of Trinidad, Quar. Jour. 

 Geol. Soc, vol. 55, p. 177, 1899. 



Guppy, B. J. L., The Tertiary Microzoic Formations of Trinidad, West Indies, 

 Quar. Jou'r. Geol. Soc, vol. 48, p. 519, 1892. 



