438 J. PrestwicHj Esq., on the 



The same author makes the average produce per acre as follows: 



Coals 31,944 tons. 



Slack (small coal) 7,986 .. 



Ironstone 13,794 . . 



These calculations were made from data obtained in Woombridge, and are consequently not ap- 

 plicable to other parts of the coal-field. In addition to these regular measures large nodules of 

 ironstone are disseminated through various parts of the strata. The ironstone of the clod coal 

 passes sometimes into a thin layer of solid ironstone. Some of the shales of the lower series, 

 especially the bituminous shale overlying the little-flint coal in Broseley arid Caughley parishes, 

 contain occasionally very large septariated nodules of ironstone, often 6 or 7 feet in diameter and 

 1 to 2 feet thick. A singular conglomerate of ironstone caps the Penneystone measure at Made- 

 ley and Lightmoor, and now and then in other localities. It forms a layer from an inch to a foot 

 thick, consisting of numerous small grains of milk-white quartz and a few small rolled pebbles of 

 ironstone and traces of trap rocks, imbedded in a matrix of ironstone. 



At Woombridge and in its neighbourhood, nodules, from 1 to 4 feet in diameter and 1 to 2 

 thick, of calcareous ironstone, inclosing curlstone, form the upper layer of the Penneystone mea- 

 sure. Upon breaking the nodules, the apices of the cones of curlstone are found generally attached 

 to the upper and lower surfaces of the crust of the nodule, whilst the bases of the cone face and 

 nearly touch each other. Some portions of the curlstone when calcined, form excellent red ochre. 



The composition of the ironstones varies, but the average produce is about S3 per cent. Two 

 or more different ores are generally smelted together. According to Mr. Anstice, the following 

 is the average proportion of fuel, flux, and ore, necessary to make one ton of pig iron : Coal, 4 

 tons ; limestone, 1 ton ; raw ironstone, S tons. The loss of weight by calcination is about 25 per 

 cent. 



For an account of the extraneous minerals found in the ironstone nodules, see Appendix B. 



The following average specific gravities of the principal ironstones, I have deduced from several 

 experiments : 



Blackstone — Donnington 3*573 



Brickmeasure — Woombridge 3*304 



Ballstone — Ditto 3*418 



White Fht—Ketley 3'501 



Penneystone — Priorslee 3*477 



Penneystone — Madelcy and Broselerj.. 3*606 



Crawstone— Z)(</o 3*687 



Large ironstone nodules overlying the 



little flint coal at the Amies 3*651 



Petroleum abounds in the central and upper portions of the field. The well-known tar spring at 

 Coalport, which had its rise in one of the thick sandstones of the central series, formerly yielded 

 nearly 1000 gallons a week; but it now produces only a few gallons in the same time. In sinking 

 a shaft at Priorslee, the 20-yard rock was so charged with petroleum, that the shaft was converted 

 into a tar well. The mineral is drawn up in a bucket, and kept in large cisterns ; but the supply 

 has much decreased. In Tarbet's Dingle is a spring of water, upon the surface of which floats a 

 small quantity of petroleum. It formerly yielded two or three gallons a day. In a pit at the top 

 of the same dingle, petroleum exuded in so great abundance from every crevice in the " little 

 coal," and from the shale forming the roof, that the colliers were obliged, in the latter case, to have 

 large plates of iron suspended over them. This inconvenience was, however, of no great extent. 

 Similar cases have occurred in working the flint coal in some of the Dawley pits. In the roofs of 



