126 ROYAL SOCIETY OF CANAVA 
Colorado, which are not very different in geological horizon from those 
of the West Indies; but in the eastern portion, both of the Dominion of 
Canada and of the United States the oil horizon is much lower, ranging 
from the Devonian formations down into the Trenton. There is a 
further difference in this respect that while the oil-bearing strata of the 
several anticlines in Trinidad and Barbados are often inclined at high 
angles, sometimes reaching the vertical, and oil in quantity is obtained 
from these highly pitched sediments, the oil-bearing strata both in 
Canada and in the United States, especially in the older series of rocks, 
generally occur with low dips or as low anticlinal domes. When these 
older rocks are steeply inclined they become faulted and the contained 
oil and gas tend to escape by such channels to the surface. The softer 
rocks of the Tertiary on the other hand appear to have yielded readily 
to the crushing forces, and faults of importance are rarely seen, so that 
the contained oil still remains in the underlying sediments and has not 
escaped along the fault planes, except as in the case of the known pitch 
or asphalt beds where probably the crests of oil-bearing sandstones have 
been denuded. 
Among other phenomena frequently seen in connection with the 
anticlines in Trinidad are the mud-volcanoes already referred to. These 
seem to be due to the explosive force of gases which have been confined 
under great pressure by the overlying strata of clays, etc. When such 
confining pressure is sufficiently weakened or the accumulated force of 
the gas becomes too great for the cover, the explosion occurs, and 
immense volumes of liquid mud are thrown out with sufficient force to 
sweep away great areas of jungle and to carry down the debris along the 
nill-sides to the sea when this is near, or to overwhelm large areas of the 
country when inland around the centres of the explosion. Gas is 
frequently seen to issue from the craters thus formed as well as along the 
lines of anticlinal structure, and pits sunk along such lines soon become 
filled, or partially so, with petroleum. 
In the comparatively brief period which could be devoted to the 
study of the geological structure of this island, it was possible merely 
to ascertain the leading features. The structure has been given with 
considerable detail in the reports published recently by the Government 
geologist Mr. Cunningham-Craig. But little attempt has, however, 
apparently been made to obtain a full collection of the organic remains 
from the Tertiary rocks, other points, especially as regards structure 
being probably regarded as of greater importance. Sufficient fossil evi- 
dence has, however, been found to determine their general geological 
position. 
