The Ironstone-Formation of the Forest of Dean; with a Sketch of the General Geology and Industrial History of the District

Abstract

The coal-measures repose conformably on a series of grit-beds, all more or less charged with oxide of iron, and measuring together about 500 feet in thickness. In some places a bed of limestone intervenes between the lowest bed and those above, but the general section, in descending order, is as follows:—1. Coarse red grit-stone, called “The Miner's Farewell Rock.”2. Light red sandstone, with layers of variegated marls, which, although partly indurated in the bed, fall to pieces by exposure to the air.3. Fine-grained quartzose grit, much charged with iron in the middle beds, constituting the “Sandstone Mine Formation.” In this group there are two thin beds of coarse conglomerate, or pudding-stone.It would be impossible for me to enter into any adequate description of this most important part of the Forest geology, without extending this article to an undue length. The following summary, therefore, must suffice, in the present instance; although I purpose describing the coalfield, which has special interest—geological as well as industrial—on another occasion.If the ordnance geological sheet No. XLIII. S.E. be examined, with the horizontal sections Nos. 15 and 16, a very good notion of this coal-basin may be obtained, although not too much dependence is to be placed, practically, on the position of the lines marking the crop of the several veins. Indeed, to lay down the line of crop accurately, in many places where there are no workings, is impossible, from the thickness of the over-burden or soil: besides which, the theoretical lines invariably require to be shifted, from the occurrence of minor faults and local denudation.