in Yorkshire and Durham. 37 
sometimes found in the crevices between the basaltic columns, 
several feet above the beds on which they rest. 
In addition to the substances above described, I found be- 
neath the trap some thin white porcellanous fragments, which 
appeared to be derived from an indurated bed of fire-clay—a well 
known associate of the great coal formation. 
All these phenomena so exactly resemble the effects pro- 
duced by fire, that I am unable to describe them without using 
language which may be thought hypothetical by those who deny 
the igneous origin of trap dykes. 
In Cockfield Fell the coal-works have been conducted on 
both sides of the dyke, and the extraordinary changes produced 
by its influence have been recorded by practical men who had no 
theory to support, and who founded their opinions upon actual 
observation. The works are not now carried on in the immediate 
neighbourhood of the dyke; but I procured so many specimens 
of the substances which had been taken from the altered coal- 
beds, that I have no doubt of the general accuracy of the accounts 
which have been published. 
Close to the dyke, the main coal is converted into a substance 
resembling soo¢, and at some distance it passes into a more solid 
substance, which the miners call cinder. At a still greater distance 
it retains a part of its bitumen, and about thirty yards from the 
trap it does not differ from the ordinary pit-coal of the district. 
It is stated, (Hutchinson’s History of Durham) “ that immedi- 
“ately above the cinder there is a great deal of sulphur in 
“angular forms of a bright yellow colour. The cinder burns 
*‘ clear, without smoke, and affords very little sulphurous effluvia.” 
Were there no other examples of corresponding phenomena feneous origin 
it would perhaps be unsafe to draw any direct conclusions from” "° “** 
the facts which have been stated. But in different parts of the 
British Isles, similar effects appear, in instances almost without 
number, to have been produced by the operation of similar 
