TERTIABY MICEOZOIC FORMATIONS OF TRINIDAD. 539 



and fragments of these, form so large a proportion of the rock that 

 it may be included among the siliceo-calcareons earths. 



If a little of the dust of the rock be examined with the micro- 

 scope under a i-inch objective, it is seen to consist mainly of frag- 

 ments of radiolaria, sponge-spicules, and some indefinite argillaceous 

 substance. The radiolaria are similar to those from Barbados. 

 Podocyrtoid forms are numerous : well-preserved specimens are not 

 uncommon. There are a few diatoms. Calcareous organisms are 

 represented by numerous small foraminifera and peculiar stellate 

 bodies similar to those from Barbados described and figured by 

 Mr. W. Hill.' 



The inorganic material forms but a small proportion of the rock ; 

 it is an amorphous argillaceous substance, often flaky. It varies in 

 colour from a reddish or pale-yellow colour to clear and colourless ; 

 it is slowly bleached in strong hydrochloric acid. It agrees in 

 general character with the " argillaceous matter " of modern deep- 

 sea deposits described by Dr. J. Murray and Prof. Eenard.^ Grains 

 of sand and other clastic material are absent. 



Pumiceous Radiolarian Marl. — A second specimen from South 

 Naparima agrees in general characters with that previously described ; 

 •the matrix, however, contains a large proportion of pumice of the 

 filamentous acid type. 



(2) ' Argiline' — a tough chocolate-coloured clay. — The specimens 

 of this rock are all tough and indurated rather than hard, and 

 they can easily be scratched with a knife. They do not effervesce 

 with acid. The rock consists mainly of fragments of an amorphous 

 argillaceous substance which varies in colour from brownish-red or 

 light-yellow to colourless and transparent. Minute granules of 

 peroxide of manganese are scattered throughout. The materials in 

 the rock are stratified. 



Fragments of radiolaria are not uncommon, but they are generally 

 indeterminable. 



Ordinary clastic material is absent, and the rock appears to be a 

 true representative of one of the chocolate-coloured varieties of red 

 clays. 



In lithological character and the condition of the radiolaria this 

 resembles an impure Ordovician chert, for a sample of which I am 

 indebted to Prof. H. A. Mcholson. The rock is, however, not 

 siliceous enough to be included among even the most impure cherts. 

 The examination of microscopic sections suggests that the proportion 

 of manganese in the rock is rather high, and it may be regarded as 

 a kind of bole. 



(3) Foraminiferal Marls of Naparima. — The finest material 

 obtained from this by washing agrees with that of the radiolarian 

 marls, but it is associated with coarser constituents. The radio- 

 larian fragments are rare, but foraminifera are larger and more 



1 See this Journal, vol. xlviii. (1892) pp. 177-178 ; Mr. Guppy refers these 

 stellate bodies to Calcaromma calcarea, Wyville Thomson (see ' The Atlantic/ 

 Tol. i. p. 233). 



'^ ♦ ChaUenger ' Eeport on Deep-sea Deposits, 1891, pp. 24-25. 

 Q.J.G.S. No. 192. ' 2p 



