Coal-basins. 



mile in length and breadth. It seems evident that these basins have 

 once been small lakes or marshes, and that the strata have been de- 

 posited on the bottom and sides, taking the concave form which de- 

 positions under such circumstances must assume : and it is deserving 

 of notice, that the stratum of coal, which in one of these coal-basins 

 at Hudswell is a yard thick in the lowest part, gradually diminishes 

 as it approaches the edges, and then entirely vanishes. This fact 

 proves that the present basin-shaped position of the strata was their 

 original one ; and that the basin, at the period when the coal strata 

 were formed, was a detached lake or marsh, and not part of the bed 

 of the sea. 



It has been supposed that coal strata were deposited on the bed of 

 the ocean ; but this is not probable, for the vegetable remains, so abund- 

 ant in the coal strata, belong to families of terrestrial or marsh plants, 

 ferns, gigantic equisetums (horsetail), with jointed and striated stems 

 like reeds, hence called calamites, and lycopodia allied to ferns i 

 these compose the greater part of the fossil plants accompanying 

 coal. In some instances, the coal is decidedly formed of such 

 plants ; and, from the plants being sometimes found erect, we may 

 infer that they grew near the place where they occur. There is a 

 .stratum of indurated shale and imperfect ironstone in the Yorkshire 

 and Derbyshire coal-fields, called muscle-bind ; it is filled with shells i 

 they resemble freshwater muscles ; and though there may be shells 

 closely allied to them in form, in some of the marine limestones^ it 

 deserves notice, that the substance of the shells in the coal shale, at 

 least wherever I have seen them in the Northern coal-fields, has that 

 cretaceous or chalky appearance and consistence, which I have ob- 

 served to be peculiar to shells in what are regarded as undoubted 

 freshwater formations. 



If the basins in which the coal strata are deposited were originally 

 freshwater lakes or marshes, did any of the plants whose remains 

 compose coal grow where the coal is now found ? or, were they 

 carried by rivers or inundations into the lakes, and gradually depos- 

 ited as the water evaporated ? The former is perhaps the most prob- 

 able hypothesis ; and the occurrence of the same peculiar kind of 

 fire clay under each bed of coal, favors the opinion, that this was the 

 soil proper for the production of those plants from which coal has 

 been formed. If we suppose that these lakes were periodically laid 

 dry, and again filled by sudden inundations, we shall have the con- 

 diuons required for the succession of carbonaceous and earthy strata 

 that take place in a coal-field : a repetition of such inundations would 

 fill up the lake or basin. Nor can such a supposition appear im- 

 probable ; for, as the species of vegetables in the coal strata are 

 analogous to what at present grow in tropical climates, we may infer 

 that they were subjected to such atmospheric influences as promote 

 the rapid growth and decay of vegetation in hot countries, accom- 

 panied with great periodical inundations, 



15 



