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tion : for we pass at once from the inclined and disrupted masses to 

 the horizontal conglomerates now resting upon them ; and there is 

 no trace of any effect that indicates a slow progress from one system 

 of things to the other. 



Lastly, we have the clearest evidence to show that these vast dis- 

 ruptions were produced during the elevation of the carboniferous 

 chain ; and, if I am not mistaken, during the same period arose many 

 minor cracks and fissures, forming the moulds into which were, in after 

 times, cast some of the richest lead veins of our island. 



It is well known that the rich carboniferous deposits of this coun- 

 try undergo a great change of structure in their range from the Bristol 

 Channel to the valley of the Tweed ; and I hope I shall not be thought 

 to wander too far from my object, if I attempt shortly to explain in 

 what the changes consist, and what are their modifications. 



All our coal formations are essentially composed of mountain 

 limestone, sandstone, and shale : they differ only in the mode in 

 which these constituents are aggregated — In the various coal-basins 

 on the Bristol Channel, the limestone-beds are developed only in 

 the lower, and the coal-bearing-beds in the upper part of the series ; 

 and the two members are separated by nearly unproductive deposits 

 of millstone-grit and shale. 



Almost in the same words we may describe the carboniferous series 

 of Derbyshire. There, however, the millstone-grit is more complex, 

 and of very great thickness ; and subordinate to the great shale are, 

 here and there, very thick masses of a peculiar, thin-bedded and some- 

 what argillaceous limestone. 



On the re-appearance of the carboniferous limestone, at the base 

 of the Yorkshire chain, we still find the same general analogies of 

 structure : enormous masses of limestone form the lowest part, and 

 the rich coal-fields the highest part of the whole series j and, as in 

 the former instances, we also find the millstone-grit occupying an 

 intermediate position. The millstone-grit, however, becomes a very 

 complex deposit, with several subordinate beds of coal ; and is sepa- 

 rated from the great inferior calcareous group (known in the North 

 of England by the name of scar limestone), not merely by the great 

 shale and shale -limestone, as in Derbyshire, but by a still more com- 

 plex deposit, in some places not less than 1000 feet thick ; in which 

 five groups of limestone strata, extraordinary for their perfect con- 

 tinuity and unvarying thickness, alternate with great masses of 

 sandstone and shale, containing innumerable impressions of coal 

 plants, and three or four thin beds of good coal extensively worked 

 for domestic use. 



In the range of the carboniferous chain from Stainmoor, through 

 the ridge of Cross Fell, to the confines of Northumberland, we have 

 a repetition of the same general phenomena. On its eastern flanks, 

 and superior to all its component groups, is the rich coal-field of 

 Durham. Under the coal-field, we have, in regular descending order, 

 the millstone-grit, the alternations of limestone and coal measures 

 nearly identical with those of the Yorkshire chain, and at the base of 

 all is the system of the great scar limestone. The scar limestone 



