]66 THE POPULAR SCIENCE MONTHLY. 



carboniferous limestone had been uplifted to sometliing near its pres- 

 ent position. B}' measuring the whole length of the succession of 

 limestone-strata that presents itself along the gorge of the Avon, and 

 making the requisite allowance for their slope, the geologist has no 

 difficulty in determining their thickness ; and he can say with cer- 

 tainty that, if these successive beds of limestone were piled horizon- 

 tally upon one another, in the same manner as when they were first 

 formed, their total thickness would exceed 2,000 feet. 



Further, you must think of these strata, not only as they present 

 themselves at the surface, but as underlying all our coal-fields, and as 

 probably extending very far beneath the newer strata to the southeast 

 of the dividing band I have just spoken of. Thus, if you look again 

 at the geological map, and notice how the gi-eat South Wales coal- 

 field is surrounded by the blue band that indicates the carboniferous 

 limestone, you must think of this limestone as really continuous over 

 the whole of the included area, since it is met with at all points in 

 which the coal-pits are sunk deep enough to reach it. And so in the 

 midland counties, where the map indicates New Red Sandstone and 

 later formations as the surface-strata, these, on being bored through, 

 are found to have coal beneath them ; and if we continue the boring 

 downward through the coal-measures, we everywhere come to the 

 limestone-base of this great and important carboniferous series. How 

 far this series extends beneath the newer deposits which form the land 

 of the southeastern portion of England, no geologist can at present 

 say with certainty. If it really underlies them, it must be at an enor- 

 mous depth, as the results of the Sub-Wealden boring have clearly 

 proved. 



Although we are accustomed to speak of the coal-basins of Nor- 

 thumberland, Durham, Yorkshire, Staifordshire, Gloucestershire, Som- 

 ersetshire, and South Wales, as distinct and separate, it is important 

 to bear in mind that they were probably continuous w^ien the coal- 

 measures were first formed, the "basins" not having then taken shape. 

 This shape was given them by the great disturbance of the older crust 

 of the earth which marked the close of the Palaeozoic period, and 

 which brought up the carboniferous limestone into the ridges that now 

 constitute the borders of the basins. 



It is this upheaval which has given us access to a vast storehouse 

 of a material of the greatest value to man. Every Bristolian knows 

 the use of this limestone, alike for building and for the making of 

 roads ; and the demand for it in tlie midland counties, to which the 

 Severn affords an easy water-carriage, hastens the already too rapid 

 demolition of his beautiful cliffs. When " burned," i. e., reduced by 

 heat to the condition of " quicklime," it becomes in virtue of its 

 peculiar power of combining with water the basis of all mortars and 

 cements. It is as indispensable to the iron-smelter as the coal by which 

 his furnaces are heated, since without its presence he could not reduce 



