[ELLs] NOTES ON GEOLOGY OF TRINIDAD AND BARBADUS 128 
Thus in the latter place the vein beginning with a thickness of a few 
feet only at the surface gradually widened till it measured not far from 
seventeen feet in places, and the deposit was workable to a depth of 1,300 
feet before the brecciated character rendered its extraction unprofitable. 
In the principal workings in Trinidad a similar enlargement occurs from 
a comparatively thin vein at the surface to over thirty feet in thickness 
at a depth of only 200 feet. In general appearance the mineral from the 
two places is very similar, both in the bright, glossy-black aspect, and in 
the large percentage of asphalt, contained in the purer portions ; but with 
this difference, that the newer or Trinidad mineral melts readily even 
with the flame of a lighted match like ordinary sealing wax, while the 
albertite is not affected to such an extent. This is probably due to the 
more altered condition of the latter, owing probably to its greater age 
and its higher state of metamorphism, in this manner forming conditions 
which in the case of coals produces anthracite at one stage and lignite 
or bituminous coal at another. 
The derivation of the Manjak from crude petroleum is well illus- 
trated at one of the shafts sunk on this mineral on the island of 
Barbados, where both boring for oil and sinking for Manjak have been 
carried on for some years. The Manjak mined in Barbados is as a rule 
in a purer condition and‘of higher grade than that found in Trinidad 
and as a consequence commands a higher price in the market. In one 
of the shafts sunk on this mineral it was found that at a depth of about 
150 feet it gave place to a thick black petroleum, which flowed into the 
shaft and has since been removed by baling. The strong inference, 
therefore, from this occurrence, as also from evidence obtained at other 
points, is that the filling of the Manjak veins is due to the inflow of 
crude petroleum in the first place from oil-bearing strata beneath. 
In Barbados, as also in Trinidad, the fissures which now contain 
this mineral seem to be caused by pressure, apparently from a north- 
west direction. In places the strata are thrown into extensive folds, 
anticlines and even overturns, so that the conditions for the occurrence 
of petroleum are not favourable in all cases. Sometimes, however, these 
disturbances are not so pronounced. As in Trinidad the fissures now 
filled with Manjak have been caused by the crushing of the softer Ter- 
tiary rocks against beds of harder sandstone and probably of limestone. 
These deposits are found at a number of points and always near the 
crests of anticlines in so fan as could be ascertained. 
A comparison of the oil-bearing rocks of these islands with those 
found in Canada and the United States shows a wide difference as to 
horizons. Thus in the western portion of the North American continent 
there are extensive oil-fields in the Tertiary and Cretaceous of Texas and 
