J. W. Davis— The Valleij of the Calder. 505 



cooling, and consequent contraction, of the whole mass. Where the 

 earth's crust is thinner than in other places, or, from some other 

 cause, happens to be weaker, it is most likely to give way, and this 

 seems to have been the case in the district which now forms the 

 range of hills westwards from Halifax. The thick beds of gritstone 

 and shales were crumpled up like the leaves of a book, but, being of 

 a hard and very inelastic nature, the grit rocks were broken asunder, 

 and we have the two faces of the separated rock considerably apart, 

 in some instances the distance has to be reckoned by miles. 



Suppose there are 10,000 feet of strata, for the action extends much 

 lower than the rocks which are visible, lying horizontally one above 

 another ; then imagine a force pressing this mass from below with 

 sufficient strength to bend or bulge it outwards, what will be the con- 

 sequence ? The stratum, which we will suppose to be a sandstone, 

 occupying the surface, will be bent upwards, until it can no longer 

 bear the strain, when it will burst or break into two parts, leaving a 

 space between. The upheaval may have been, in all probability was, 

 a very slow process. It is not at all necessary to suppose that the 

 movement was a rapid one, or that it took the form of a gigantic 

 earthquake or other cataclysm of that nature. The pressure may 

 have been gently but persistently applied, and the operation have 

 extended over ages. As the strata were successively strained and 

 broken, they would gape wide apart at the centre of the arch ; each 

 bed of sandstone or shale, as it became elevated to the surface, 

 would carry those which had preceded it further and further from 

 the centre of rupture. This is the kind of action which actually 

 occurred during the elevation of the Pennine Chain. If any one, 

 walking from Halifax to Blackstone Edge, took the trouble to notice, 

 be would find that he passed over the several outcrops of the Rough 

 Eock and Flagstone, which presents an escarpment to the westwards, 

 where its existence terminates; then the series of Third Grits, which 

 are greater in number, but not so thick and important as the rocks 

 above and below ; and finally the great precipitous cliffs of the 

 Lowest or Kinder Scout Grits would be found terminating abruptly 

 on the summit of Blackstone Edge, forming the boundary of the 

 county. 



Between each of the escarpments of sandstone, a much more even 

 tract would be passed over, which on examination would be found to 

 be shale. 



We have now glanced, very briefly, over the physical contour, 

 the geological structure, and the internal displacement of tlie rocks, 

 forming the surface, and we know now what kind of material the 

 physical forces, some extinct, others in daily operation, have to work 

 upon. 



It has already been observed that the bed of the river, from 

 Sowerby Bridge eastwards, runs through a series of somewhat level 

 plains, not unlike the appearance that would be presented by a 

 string of lakes joined together by a broad river. Where the structure 

 of these level tracts has been exposed, by sinking wells or other 

 means, it has been found to consist of sand containing a great 



