^<^1« 55-] ^^^ OCEAI*]-IC DEPOSITS OP TEINIDAD. 177 



10. The Oceanic Deposits of Tkixidad (Bhitish West Indies). 

 By Prof. J. B. Harrison, M.A., F.G.S., P.C.S., & A. J. Jukes- 

 Beowne, Esq., B.A., P.G.S. (Eead January 4tli, 1899.) 



I. Historical Introduction. 

 [By A. J. Jue:es-Browne.] 



Tee object of this communication is to present some observations 

 on the succession and geological relations of the beds which have 

 long been known in Trinidad as the J^aparima Marls. This 

 name was given to these beds by Wall & Sawkins in 1860,^ on 

 account of their occupying a large part of the l^aparima district, 

 east and south-east of San Fernando (see map, fig. 1, p. 182). 



The beds so named formed one of the five series which were 

 described by these authors under the head of the ' iSTewer Parian 

 Group.' The names given to these five series were {a) IS^ariva 

 Series, (6) jSTaparima llarls, (c) Tamana Series, {d) Caroni Series, and 

 (e) Moruga Series ; but it was explained on a subsequent page ^ that 

 these subdivisions do not form a definite succession. The jS'ariva 

 Series occupies a central or axial position, and this Wall & Sawkins 

 considered to be the oldest. The Tamana and the Caroni Series 

 occur only to the north of it, while the Nariva and the Moruga lie 

 on the southern side, and they thought that these two sets of 

 deposits might be correlative one with another, the Nariva corre- 

 sponding to the Tamana and the Moruga to the Caroni Series. 



In their general section across the island from north to south, 

 Wall & Sawkins show the iN'ariva Beds dipping southward below 

 the ISTaparima Marls, and the latter passing in the same direction 

 beneath the Moraga sands ; while still farther south they indicate 

 a syncline occupied by jSTaparima Marls which rest directly and 

 unconformably upon the ' Older Parian rocks ' (i*^eocomian). Thus, 

 in the opinion of the above-mentioned authors, the sequence within 

 their Newer Parian Group was as follows : — 



(3) Caroni — Moruga Series. 

 (2) Tamana — Naparima Series. 

 (1) Nariva Series. 



They describe the Naparima Marl as ' a series . . . composed of 

 marls, conglomerates, and calcareous sand.' They speak of the 

 marls as fine-grained deposits varying from argillaceous marls to a 

 deposit with ' a basis of siliceous substance, consisting of the shields 

 of infusoria ' with about 20 per cent, of carbonate of lime. They 

 state further that * the best agricultural variety is the white marl 

 of South Naparima, which is very light, softer than chalk, and of an 

 extremely white colour.' ^ It is therefore perfectly certain that what 

 are now known to be radiolarian and diatomaceous marls constitute 

 an essential part of the Naparima Marls. 



The position of the conglomerates is not indicated, except that 



^ Mem. Geol. Surv. ' Report on the Geology of Trinidad,' p . 35. 

 2 Ibid. p. 59. 3 jj^YZ. p. 36. 



Q. J. G. S. No. 218. N 



