90 



COLLIERIES NEAR SHREWSBURY. 



some few species in other classes of the animal kingdom are known to have lived on 

 through various successive periods, each species of ichthyolite is supposed by that author 

 to be peculiar to the formation in which it is found imbedded. Now, in the preceding 

 chapter, it has been shown, that the formation of the lower New Red Sandstone, having 

 a maximum thickness of nearly one thousand feet, is interpolated between the magnesian 

 limestone and the coal-measures, in both of which formations, thus widely separated, we 

 now find the same species of fish. It has, however, been my object to show, that no 

 violent interruption of the series of deposits of this age has occurred in Shropshire or 

 Staffordshire ; and hence we might well imagine, why under such conditions, animals 

 of the same species should have continued to exist during a very long period. But 

 at Manchester, the stratigraphical relations are different from those described in the 

 central counties ; the red sandstone and marls, including the equivalent of the magne- 

 sian limestone before mentioned, being ^conformable to the upper coal measures and 

 freshwater limestone : yet notwithstanding this dislocation, which interrupts the perfect 

 sequence of deposits, there is still a complete transition in mineral type and organic 

 contents. 



After this comparison of the most interesting features of the Shrewsbury and Man- 

 chester coal-fields, I will now revert to the detailed description of other phenomena in 

 rocks of this age in Shropshire. 



Although it has been stated that for the most part the strata in the Shrewsbury coal-field are 

 seldom inclined more than five inches in a yard, as at Pontesbury, there are exceptions to this 

 rule, particularly at the extreme end of the zone at Coed Way, where the coal dips at a high angle 

 beneath the oldest members of the New Red Sandstone and Dolomitic Conglomerate. Among 

 the numberless faults which affect the strata, the chief one at Pontesbury runs from north-north- 

 east to south-south-west and is a downcast of seventeen yards on the dip, whereby the limestone is 

 thrown down nearly to the level of the thin or lower coal. (PI. 29. fig. 8.) 



As this zone of the coal approaches Shrewsbury it becomes thinner and more disjointed. It is 

 now worked at Ascot, and was in former times extracted at the Moat; a patch of it forms a broken 

 and elevated trough extending to Longden, where the coal rises to within a few yards of the surface, 

 but is not worked, and rests upon purple greywacke grits of the Cambrian system. The latter rock 

 here advances from the Longmynd and Linley Hills into the narrow promontory of Lyth Hill, 

 round which the narrow zone of coal-measures is folded, and occasionally rises, as at Longden, to 

 some height. This purple greywacke is the irregular base on which this part of the coal-field rests, 

 and hence the coal which occurs at one spot, in consequence of the older rocks lying at certain 

 depths, is cut out at other points by the protrusion of these ancient formations. Along the western 

 edge of this promontory the coal-measures as they advance towards Shrewsbury continue to be in 

 a very broken condition. The upper coal is the only seam which has been found in this quarter, 

 most of the old works at Wellbatch, the Moat, and Sutton having effected little more than clearing 

 away the basset edges of the mineral as it rose up on the sides of the underlying Cambrian rock. 

 Mr. Hughes of Wellbatch, however, has made, and is still occupied in making trials upon the dip of 

 these beds by which the coal has recently been won beneath the Lower New Red Sandstone. Though 



