1856.] BOWEN TRINIDAD. 389 



4. On the Geology of Trinidad. By H. G. Bowen, Esq., F.G.S. 



[Abstract.] 



The northern district of the Island of Trinidad, with the islands 

 between it and the mainland, is composed of flagstones, slates, and 

 schists, with qnartz- veins and some dark- coloured intercalated lime- 

 stone. These rocks are all apparently unfossiliferous ; the slates 

 often abound with iron-pyrites and magnetic iron-ore, and some of 

 the ochreous quartz-veins (gossans) are sHghtly auriferous. Stalac- 

 titic caves occur in the limestone of the Island of Gaspar Grande, 

 and at Las Cuevas and Arouca. Alluvial beds of clay and gravel 

 are extensive in this district, and are sometimes 60 feet thick. At 

 Lateen Bay, in Chicachicare Island, a patch of aluminous clay-slate 

 occurs, with seams of crystalline limestone. The soil of this northern 

 district is fertile on the limestone, and barren on the slates. The 

 slate-rocks appear to be the same as those of Venezuela, which ovfer- 

 lie the quartz-rock that crops out at Upata ; and rounded boulders of 

 quartz-rock occur in the flagstones. 



In the south of the Island of Trinidad, red sandstone abounds, 

 often ferruginous, and associated with clays which are often either 

 bituminous or pyritous, and contain lignite and impressions of dico- 

 tyledonous leaves. In the Erin district the clay-beds have been 

 sometimes indurated and jasperized by heat. They afibrd also small 

 aluminous, chalybeate, and sulphuretted hydrogen springs, and in 

 the blue-clay formation are found hillocks throwing up mud and 

 water, and ponds covered by a film of mineral tar. The mud-vol- 

 canos throw up saline water and greyish mud, in a cold state, with 

 iron-pyrites and water-worn pebbles of blue hmestone like that of 

 the northern part of the island, and sometimes of sandstone. They 

 do not appear to be connected with the sea ; and are most active at 

 the close of the rainy season. At Moruga small hills of granular 

 limestone occur. The succession of deposits in this southern part of 

 Trinidad appears to be — beginning from below — 1 . Sandstones, varie- 

 gated sands, Kgnitiferous clays (sometimes jasperized), and the Mo- 

 ruga limestone ; 2 . Blue and brown clays, with bitumen ; comprising 

 the pitch-lakes, salt and alum springs, &c. ; 3. Modern marine sand 

 formation, from 50 to 100 feet thick; and alluvial deposits, seldom 

 more than 30 feet thick. 



The eastern coast of Trinidad appears to consist of the red sand- 

 stones and bituminous clays as far north as Matura, beyond which 

 the clay-slates set in. 



The western coast of the island, south of Port of Spain, which is 

 built of the slate-rocks and limestone, exhibits only modern alluvial 

 deposits, sometimes calcareous, frequently ferruginous, and appa- 

 rently resting towards the south on the red sandstone of the southern 

 district. 



