526 ME. E. J. LECHMEEE GUPPY O'N THE 



The proportion of lime in the argiline is greater than is here 

 shown. The report states that the portion selected for analysis 

 was free from calcspar. But this mineral exists in minute veins 

 traversing the rock, and is derived from the solution and redeposi- 

 tion of the calcareous matter of contained organisms. The above 

 analyses show much resemblance in the composition of the two 

 rocks. 



Now, as to the argiline,^ considerable variation exists in different 

 specimens of it, but the following characters apply generally : — It is 

 extremely fine-grained aud readily abrades the teeth of a file. 

 While chiefly a siliceous rock, it contains a notable quantity of lime 

 and a certain proportion of alumina. The calcareous matter is 

 either disseminated through the rock (probably its original condition) 

 or it exists in the form of minute veins of calcite as above men- 

 tioned. The rock has a lamination resembling cleavage, but this is 

 crossed again by joints approximately at right angles to the planes 

 of lamination and to each other, so that it breaks up into irregular 

 prismoidal masses, varying much in size in different beds, but ranging 

 generally from 1 inch in length by | inch in breadth and thickness 

 to three or four times those dimensions. The fragments are often 

 nearly white or of a pale buff externally, but on being fractured 

 they are found to be of a deeper colour internally. The paler ex- 

 ternal colour is due to the dissolution of the iron by water. Water 

 percolating through the joints slightly softens the surface of each 

 prismoidal piece and removes some of its constituents, but penetrates 

 only to a very slight distance. Nevertheless, a gradual disintegra- 

 tion takes place in the outer and more exposed portions of the rock. 

 The lime and iron are carried off in solution, and partly re-deposited 

 in the joints as fine veins of calcite and black films and dendritic 

 markings of iron. The prismoidal pieces into which the rock sepa- 

 rates are hard and tough and require a smart blow of the hammer 

 to break them. The material is largely used for road and railway 

 metal. For the first-named purpose it is not so good as some 

 varieties of limestone ; for it rapidly crumbles into dust under the 

 ordinary road traffic. But for railway purposes it is probably un- 

 surpassable. 



The origin and nature of this argiline are somewhat problema- 

 tical. No distinct traces of organisms are visible in it. Washing 

 reveals no foraminifera or other fossils. Unlike the South Naparima 

 marl no radiolaria or diatoms are developed by treatment with acid 

 or otherwise. Thin slices,; however, show the existence of minute 

 cavities which are the casti of fossils the original matter of whose 



1 In the Geological Eeport on Trinidad (p. 33) the name ' argiline ' was 

 applied to the rock of Naparima Hill and other localities. The definition given 

 wasas follows : — " Strata composed of an argillaceous base, with small equivalents 

 of carbonate of lime and free silica." This account by itself alone is scarcely 

 satisfactory. The additional particulars now furnished will aid in giving an 

 idea of the nature of the rock. One use of the material will no doubt be for 

 polishing purposes. 



