356 Mr. Weaver's Geological Observations on 



sandstone, in driving the Bullo Pill Tunnel, which traverses Hay hill near 

 Newnham, being about 1200 yards in length. 



§ 36. In ascending the north-eastern escarpment of the Forest of Dean 

 coal-basin from Mitchel Dean, we find the old red sandstone supporting the 

 carboniferous limestone, both dipping 60° toward the south-west ; toward the 

 escarpment on the north-western side of the basin, as at the Trigg quarries, 

 the general dip is 45° toward the south-east; but at the northern end of the 

 ellipsis, and in the escarpment below the elevated and prominent point of Lea 

 Bailey hill, the dip is 20° to 25° toward the south ; so that here, as in the 

 Cromhall coal-basin, the lowest angle is found at the northern end of the 

 basin, while on the south-east and south-west the strata gradually acquire a 

 greater elevation. In the tract extending from the foot of the northern 

 escarpment to Perrystone hill on the north, a distance of six miles, the old red 

 sandstone is still found, dipping at first 20° to the south, but subsequently it 

 becomes almost horizontal, or gently inclined to the south-west or west. 



§ 37. The old red sandstone displays here, in general, the same characters 

 as have been described in speaking of the environs of Tortworth, including 

 also some subordinate beds of sandstone conglomerate. 



The carboniferous limestone may be distinguished into two masses, a lower 

 and an upper one. The former is composed of blueish-gray compact limestone 

 in frequent alternation Avith beds of slate-clay and marly clay ; the organic 

 remains contained in which are analogous to those met with in the Tortworth 

 district : — among these are found also remains of the Rhodocrinites verus and 

 Cyathocrinites planus. The upper and more considerable mass consists of 

 magnesian limestone, fine and minute foliated granular, and of purplish, red- 

 dish, yellowish, and grayish colours, disposed in continuous strata, and free 

 from other beds. Haematitic iron ore is found in the magnesian limestone, 

 and has been wrought by mining operations at various periods. 



The limestone supports the bed of sandstone and sandstone conglomerate 

 which forms the immediate base of the Forest coal-basin ; in this respect also 

 coinciding with the relations of the Cromhall coal-field. 



According to Mr. D. Mushet of Coleford, the beds of the Forest coal forma- 

 tion are between 300 and 400 fathoms thick, in which are distributed twenty- 

 eight seams of coal, constituting together a body 50 feet 5 inches thick. Of 

 these, fourteen seams vary, from 1 foot 10 inches to 5 feet in thickness, forming 

 together 36 feet 7 inches of coal. The remaining fourteen seams vary from 

 4 inches to I foot 6 inches in thickness. 



