410 A Gcognoslical Sketch of [Dec. 



Article II. 



A Geognostical Sketch of the Comities of Northumberland, Durham t 

 and Part of Cumieriund. By Thomas Thomson, M.D. F.R.S. 



(With a Map.) 



{Concluded from p. 316.) 



II. The second formation to which I give the name of Newcastle 

 Coal Formation, is of much more limited extent than the preceding. 

 It begins at Morpeth, or a little to the north of it, and extends, I 

 suppose, as far south as the river Tees; though of this I am not 

 quite certain, as I did not examine that part of the country myself. 

 It extends about ten miles west from Newcastle. Its western 

 boundary in the county of Durham, as marked in the map, is pro- 

 bably near the truth, as it was pointed out to me by some of the 

 mining agents, who had the best opportunity of being acquainted 

 with that part of the country. This formation in fact possesses the 

 characters of the Independent Coal Formation, as well as the pre- 

 ceding; but I was led to consider it separately, because the galena 

 veins do not penetrate it ; a demonstration that it must have been 

 deposited at a very different time from the preceding formation. 



The beds of which it is composed, like those of the preceding 

 formation, dip towards the east, and crop out towards the west, so 

 that in various places the beds of coal may be found at the surface. 

 Though I was at considerable pains to procure information respect- 

 ing this formation, and though many facts were stated to me by 

 gentlemen on whose veracity and intelligence I think I may rely, 

 vet I do not conceive myself so well informed respecting it as I am 

 respecting the preceding formation. I shall state, however, what I 

 conceive to be its structure. 



The beds are 82 in number, and consist only of three different 

 hinds of minerals ; namely, coal, sand-stone, and slate-clay, which 

 alternate with each other a great number of times. No lime-stone 

 occurs in it, nor any green-stone or basalt, except in veins which 

 traverse it, and which I shall afterwards notice. 



1. It is not easy to determine the number of beds of coal, on 

 account of the different depths at which the same bed occurs in 

 different parts of the mining field, and on account of the various 

 slips occasioned by the veins or dykes which traverse the formation. 

 I conceive the whole number to amount to 25 beds ; but a consi- 

 derable number of these are insignificant in point of thickness. 

 The two most important beds by far are those distinguished by the 

 names of High Main and Low Main. The thickness of the first is 

 six feet, that of the second six feet six inches. The Low Main is 

 about GO fathoms below the High Main. Between them occur eight 



