in Yorkshire and Durhan. 39 
im many of the lower regions it is buried in diluvium. On this 
subject there is, I believe, no difference of opinion. 
(3) There is every reason to believe that it has been filled 
from below. For there exists no trace of any upper bed from 
which its materials could have been supplied; and in one place, 
horizontal beds of sandstone rest on the top of a mass of trap 
which is probably connected with the dyke. We may further 
state, that many dykes of similar origin wedge out before they 
reach the surface *. 
(4) The dyke has once been in a fluid state. For it. is 
moulded to all the flexures of the chasm which it {fills up. The 
same assertion is also proved by its crystalline texture. 
(6) The materials of which it is composed are the same with 
those which abound in a great many varieties of recent lava, On 
this subject there is perhaps no difference of opinion. For the 
Wernerians at one time asserted, that recent lava was derived 
from the igneous fusion of trap rocks of aqueous origin. 
(6) The effects produced by the dyke are such as might be 
expected from the intrusion of a great mass of ignited matter. 
This assertion is fully established by the facts which have been 
already stated. 
If, therefore, similar effects have originated in similar causes, 
we must conclude, that this dyke, as well as all the other simi- 
lar masses in the great Durham coal-field, are the undoubted 
monuments of ancient volcanic action. 
It is a matter of fact, which is independent of all theory, 
that an enormous mass of strata has been rent asunder ; and it 
is probable that the rent has been prolonged to the extent of 
fifty or sixty miles. If we exclude volcanic agency, what power 
im nature is there capable of producing such an effect? By sup- 
iy pee et ee ee ee a 
* See Professor Henslow’s paper on the Isle of Anglesea; Dr. Mac Culloch on the 
Hebrides, &c, &c. 
Conclusion. 
