[ELLs ] NOTES ON GEOLOGY OF TRINIDAD AND BARBADOS 121 
A peculiar and striking feature of the surface is the growth of 
vegetation at different points. This is due doubtless to the presence of 
sands, blown from the surrounding shores, which have filled some of the 
numerous fissures and formed small oases on which the vegetation has 
taken root. Some of the trees on the present surface of the asphalt are 
from twenty to thirty feet in height. In some of the fissures small 
fishes, from one to two inches in length were observed. 
Among the more probable theories which have been propounded to 
account for this extensive and remarkable deposit is that which regards 
it as marking the site of an ancient mud-volcano of which the Pitch 
Lake now occupies the centre. In support of this view is the fact that 
the lake is roughly circular and basin shaped, having a depth near the 
centre of over 135 feet as reported from actual measurements by boring, 
and with gradually shelving or sloping sides. In this case the original 
mud volcano must have been of large dimensions, but at several points 
along the southern and eastern parts of the island, and near the lines of 
anticlines there are other mud-volcanoes some of which are of like large 
dimensions. 
In none of these, however, are there the same occurrences of asphalt 
as at La Brea, though there are numerous indications of gas and petro- 
leum. Another feature in favour of this mode of origin is in the fact, 
that in so far as could be observed the lake itself is situated somewhat 
to the north side of the direct line of anticline. 
Another theory recently propounded accounts for its origin on the 
supposition that it may indicate the removal of the outcropping crest 
of the La Brea anticline at this point near the west coast, and that this 
denudation has assumed a basin-shape, into which the petroleum con- 
tained in the surrounding oil-bearing sand stone and shale, which are 
extensively exposed in the vicinity, has flowed owing to the natural ten- 
dency of oils contained in porous rocks to rise to the surface. In either 
case the volatile portions of the mineral have long since been evaporated 
and the asphaltic base has remained in the more or less solid condition 
now seen. Upon either theory the presence of the lake body must be 
the result of such inflow of the crude petroleum from the surrounding 
rocks. It is also quite probable that a certain amount of liquid petro- 
leum still enters the basin from the bottom or sides of the lake, so that 
the loss incurred by the overflow in former years or by the extraction 
recently is thus to some extent compensated. This quantity in recent 
years has not, however, been sufficient to counterbalance the loss incurred 
in the mining of this deposit, since according to accurate measurements 
taken at regular intervals, there has been a slow but regular lowering 
of the original surface level, amounting within the last fourteen years 
