On the Origin of Certain Concretions in the Lower Coal-Measures

Abstract

In certain restricted areas of the Lower Coal-Measures at Halifax in Yorkshire and at Oldham in Lancashire, and in a seam of coal called the ‘hard-bed coal,’ peculiar nodules or concretions occur. These concretions, termed locally ‘coal-balls,’ are disseminated throughout the coal, not in particular lines but quite indiscriminately. They are spherical or ovoid, sometimes slightly flattened, and externally—by contact with the coal—they have been blackened; though when broken open they are found to be pale or dark brown internally, and often streaked with veins of iron-pyrites. Some years ago I made analyses of two of these concretions, and the results are tabulated below :— From these figures the constitaenta of the coal-balls are calculated to be :— The nodules or ‘coal-balls’ are of great interest, because they contain extremely well preserved vegetable remains, sections of the concretions revealing the internal structure of Coal-Measure plants in a very remarkable manuer, and it is from such sections that our knowledge of the structure of the Carboniferous flora has been largely increased. In many cases it is easy to detach large pieces of fossil wood from these concretions. Several samples of this fossil wood have been analysed by me with the following results:— The constituents of the samples of fossil wood may be calculated as follows :— From the foregoing analyses it is apparent that the fossil wood and also the concretions themselves are made up very largely of two constituents—calcium—carbonate and iron-pyrites; and that there is great variation in their relative