internal Structure of the Magnesian Limestone. 61 



further borne out by the workings of the Whitehaven field ; some of the 

 richest of which are sunk through a covering of magnesian limestone. 



Within the limits of this formation many more works will be undoubtedly 

 attempted when our present fields begin to be exhausted. Its unconformable 

 position will, however, throw great difficulties in the way of such under- 

 takings ; for in the districts where it is present, the surface of the ground 

 can seldom give any indication of the contour of the carboniferous beds 

 below, or of those flexures and dislocations by which they may have been 

 affected; and without such knowledge mining operations must often end in 

 disappointment. 



Considered on a great scale, the magnesian limestone in the county of 

 Durham may be described as a dam passing over the south-east side of the 

 coal basin, and cutting it off from all direct communication with the sea, ex- 

 cept in two places, where the dam is broken through by the channels of the 

 Wear and the Tyne. The richest parts of the coal-field bordering on these 

 rivers are already beginning to be exhausted ; and some of the more remote 

 parts are, by means of rail-roads, now brought into communication with these 

 navigable outlets. 



The rail-road from West Auckland to Stockton is twenty-three or twenty- 

 four miles in length ; and the coals are dragged out of the basin by a fixed 

 steam-engine, over an elevation which is 472 feet above the high-water mark 

 at Stockton. 



At the single pit of Hetton-le-Hole (the works of which are carried on 

 both in the High-main and Hutton-seam), more than a thousand tons of coal 

 are each day raised to the surface*. After being driven by moveable steam- 

 engines along the base of the magnesian terrace, they are, by the power of 

 two fixed engines dragged to the top of it, along a system of inclined planes 

 which reach an elevation of 350 feet above the first level from which they 

 started. From thence they descend along a second system of inclined planes, 

 and are afterwards rapidly transported by moveable steam-engines to the 

 banks of the Wear. 



An excellent line of communication (and as far as regards the mere trans- 

 port of coals to the coast, a much better one than that which has been effected 

 from West Auckland) might be established between Stockton and a rich part 

 of the coal-field, through a natural depression of the limestone terrace imme- 

 diately to the south of Howlish Hall, 



But the singular denudation of Thrislington gap (where a chasm has been 



* These facts relate to the state of the colliery in the summer of the year 1826. 



