398 New Piiblkations. 



useful illustrations of the relations of trap-rocks to the secon- 

 dary strata. At the Ratcheugli Crag the trap presents one of 

 those alternations with limestone, so frequently met with in 

 Scotland, the country of all others in this island the most in- 

 structive in regard to the geological history of secondary trap 

 rocks. The Ratcheugh Crag trap-rock we suspect is not ba- 

 salt, as mentioned by Mr Forster. — Mr Patinson's notice of 

 the hazel-nuts found in a vein of lead-ore, corrects a mistake 

 which we know has also been committetl in other mines. But 

 the most extensive and important memoir, is that entitled 

 " Obsen-ations on the South Welsh Coal Basin, by Mr Francis 

 Forster." This coal field, or basin, affords not only numerous 

 beds of common bituminous coal, but also beds of glance-coal, 

 or anthracite ; and the quantity of ironstone it contains is so 

 vast, that nearly one-third of the immense supply of British 

 iron is raised, smelted, and manufactured within its circum- 

 ference. Mr Forster also remarks that it is the source from 

 which the Cornish mines derive their supply of coal, and is the 

 market to which London must look for a supply, whenever 

 that period arrives that the coal of our northern districts either 

 becomes so scarce, or is so difficult and expensive to procure, 

 that it cannot compete with that of Wales. The sides of the 

 coal basin are of mountain-limestone, which rests upon the old 

 red sandstone. The coal formation exhibits the usual rocks 

 and alternations. In some places the position of the strata 

 appears changed by some action alter their deposition, in others 

 natural unaltered wavings of the strata occur. The quantity 

 of carburetted hydrogen gas occurring in the Welsh collieries 

 is very trifling, as compared with the Durham and Northum- 

 berland districts : this, Mr Forster remarks, may in some de- 

 gree arise from the greater inclination of the strata allowing 

 the gas to find its way to the surface between the planes of 

 the different beds; that it cannot be altogether attributed to 

 the great inferiority of the Welsh coals, for the artificial pro- 

 duction of gas is evident, from the remarkable fact, that the 

 glance-coal (stone coal) seams generally abound more in ^re- 

 damp, than the seams of bituminous coal. In regard to the 

 quantity of coal in the whole basin, Mr Forster calculates, it is 

 true in a rough way, that it may amount to about sixteen f7iou- 



