1880.] 489 [Crosby, 
Rocks similar to the itacolymite, schist, and limestone series are 
known to occur in South America beyond the limits of Brazil. They 
constitute the main mass of the great ea8tern branch of the Andes, 
or at least of that part of it which skirts the Caribbean Sea from Ca- 
raccas eastward, and is known as the littoral cordillera of Venezu- 
ela. The cordillera forms the Northern Mountains* of Trinidad, 
which have an altitude of three thousand feet, and terminates on the 
neighboring island of Tobago. These semi-crystalline rocks of the 
Spanish Main and Trinidad were studied some twenty years since 
by Messrs. Wall and Sawkins, by whom they were designated the 
Caribbean group, more recently by Mr. R. J. Lechmere Guppy, and 
in 1878 by the present writer. 
The structure of the Northern Mountains of Trinidad is mono- 
clinal, high southerly dips being the universal rule. The thickness 
of strata exposed is not less than ten thousand feet, and it may 
greatly exceed that estimate. The Caribbean group here includes 
three divisions, which, beginning with the oldest, present the follow- 
ing general lithological characters : — 
1. Quartzite, in heavy beds, fine grained, and usually more or 
less micaceous. 
Hydromica schist, which shows frequent passages into quartz- 
_ite and argillite. 
‘The argillite is abundant, and is often black, carbonaceous and 
lustrous. 
2. Crystalline limestone, in massive beds, having in the aggre- 
gate a great thickness (several thousand feet), varying in 
color from white to nearly black, sometimes decidedly ferru- 
ginous, and often with scattered spangles of silvery-white 
mica. ‘This calcareous or middle division is the highest, 
in a topographical sense, forming the crest of the mountains 
at most points. 
3. Frequent alternations of the following rocks : — 
Argillites similar to those in the first division, frequently 
graphitic, and often passing into hydromica schist, which is 
less distinctly micaceous than below the limestone. 
Hard sandstone, sometimes approaching quartzite, and occa- 
sionally decidedly ferruginous. 
Conglomerate, with pebbles of quartzite apparently derived 
from the first division. The conglomerate is not abundant. 
Thin beds of calcareous matter toward the top. 
