1G4 Mr. Williamson Peile's Description of a Group of Dykes. 



Avith which they run will at once be seen by an inspection of the plan, 

 and the course by compass is about north 10° west. 



The general course of the large Dykes in this district, it may be ob- 

 served, is north and south ; small deviations to the east and west being 

 however commonly found. The course of the 12-fathom Dyke may, 

 therefore, be considered as rare. 



I have not thought it necessary to lay sections of more than one Ri- 

 der before the Society, as that will be sufficient to give a general idea 

 of their nature ; and from the great variety of their appearance, it 

 would be useless to attempt more. It may, however, be well to add 

 that I have not been able to detect in any other, that curious branching 

 to the left, which characterizes the profile No. 1. In general, they are 

 thicker, and the Stone most free from mixture with the Coal about the 

 middle of the seam, and it is near the roof and thill that the singular 

 confusion of Coal and Stone is found. Large insulated pieces of Coal 

 resembling those in the section, are of common occurrence. 



The question which naturally arises on examining these singular dis- 

 locations, viz. as to their origin, is one which, I doubt, must long re- 

 main in the deepest obscurity. That a connection exists between them 

 and the Upcast Dykes is, however, evident from their position, and 

 that the cause has not been igneous, is proved by the perfection of the 

 insulated and mixed pieces of Coal. Such appear the only data ; and 

 to comprehend them, we are forced to revert to that time, when the 

 now solid stratum of Coal must have been so far in a fluid state as to 

 receive and retain the shape impressed on it by the more hard and 

 dense substance of the Sandstone. 



P. S. The accompanying Plan, (No. 1. PI. XIV.) shews the extent of 

 the workings up to the period of its being engraved, in the month of 

 October, 1800. 



