226 A POPULAR SKETCH OF THE 



and the distance between each bed of coal is pretty much the same 

 in one part as in another. The beds, however, of shale and grit 

 which lie between the coal seams are very irregular in their extent : 

 a bed of gritstone, perhaps, which in one place is of great thickness 

 and occupies almost the whole space detween two particular beds of 

 coal, shall in another a few miles distant be found to have thinned 

 out to a few feet and its place to be almost entirely occupied by 

 shale. This regularity and constancy over a wide area in a thin 

 bed of coal, and the irregular thickening and thinning out of the 

 shale and grits, evidently points to a difference in the conditions of 

 their deposition. The coals seem to have been deposited during a 

 period of tranquillity, in which the vegetable matter had time to 

 diffuse itself equally over the whole space occupied by the water 

 which contained it, while the shale and grits were swept in by cur- 

 rents which piled one material in one place and left another bare to 

 be occupied by another material brought in perhaps by a different 

 current. 



This irregularity in the different beds is only apparent when they 

 are traced over a great extent of country : locally they are regular 

 enough ; and we find the gritstones forming at the surface longitu- 

 dinal ridges (running about north and south) on which the soil is 

 light and fertile, with valleys or flat lands of shale, where it is fre- 

 quently cold and barren.* These cold and barren spots can often 

 be improved only by thorough draining, and this the miner most 

 effectually performs ; and by carefully preserving the vegetable soil 

 and respreading it when he has passed through the ground, tracts of 

 land are often rendered fertile which by any less efficient process 

 would always have been unproductive. This necessary precaution 

 is in other places too often neglected 



The total thickness of the coal measures in Derbyshire is very 

 great, certainly not less than 2,000 feet, of which about sixty-five 

 feet consist of coal disposed in many beds. So that if we could see 

 the whole exposed in one great cliff, we should see a huge mass of 

 shales and sandstones, in which the coals would shew like thin black 

 seams or streaks, or as dark partings between the thickened beds of 

 the other materials. 



As we descendt towards the lower part of the coal measures, we 



" No coal field with which I am acquainted can compare with that of Der- 

 byshire, for the pleasantness of its aspect, owing to the many ridges of grit- 

 stone. 



+ As far as regards the level of the country, this would be ascending; as 

 where the lower portions of the coal measures come out to the surface, they 

 form much higher ground generally than the upper portion. 



