LOWER COAL MEASURES. 



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has termed the main fault. Thin patches of coal, similar to that of Tasley, occur at Caughley and 

 at Kingslow, in both of which places the same band of limestone, four to five feet thick, occurs 

 overlying the lower coals and rising almost to the surface. The beds dip to the east at Kingslow and 

 to the north-east at Caughley, and on the whole may be said to have a slight easterly inclination. 



We thus find this very remarkable band of freshwater limestone in situations more 

 than thirty miles from its western termination near the Breidden Hills, again associated 

 with coal and passing upwards into the Lower New Red Sandstone ; and hence it is 

 clear, as inferred in the last chapter, that we must consider the zone to which this lime- 

 stone is subordinate, as the youngest member of the carboniferous series. Neither the 

 coal, limestone, nor any one of the associated strata in these deposits is of great per- 

 sistency, hut each of them thins out and reappears at intervals. The poor and detached 

 coal-hearing strata to the south of Bridgenorth, which dip away from the Old Red Sand- 

 stone, and have been already alluded to as rising conformably from beneath the Lower 

 New Red Sandstone of Chelmarsh, are for the most part of the age of those at Tasley 

 and Caughley, and will be subsequently described in conjunction with the coal measures 

 of the Forest of Wyre 1 . 



Lower Coal measures or productive Coal- and Iron-Jield. — After this supplementary ac- 

 count of the strata composing the upper coal measures described in the previous chapter, 

 and to which the attention of geologists has never yet been sufficiently directed, the fol- 

 lowing very brief sketch of the lower or great productive mining portion of this valuable 

 tract may be sufficient ; for, it is not easy to give a very precise notion of the structure 

 of this portion of the field without entering into a variety of details foreign to my 

 purpose. The labours of Mr. Prestwich, however, teach us, that the mineral cha- 

 racters of the same strata often change completely within very short distances, beds 

 of sandstone passing horizontally into clay, and clay into sandstone ; that the coal seams 

 wedge out or disappear ; and that sections at places nearly contiguous, often present 

 the most marked lithological distinctions. These observations, which coincide with 

 my own in various other coal-fields, demonstrate the hopelessness of determining the 

 respective ages of such rocks in different localities by shaft, sections, or a mere com- 

 parison of their mineral characters. Even the coal itself constantly tapers away and 

 disappears amid the shales and sandstones, constituting what are locally termed "Symon- 

 faults," the character of which, as distinguished from true faults, is explained in the 



1 Mr. Prestwich has informed me that a shaft has recently been sunk near Broseley, which after passing 

 through ninety yards of slightly productive upper coal measures, reached a bed of limestone four yards thick, 

 identical in structure with, and containing the same microscopic shells as, the Shrewsbury limestone. (April, 

 1837.) 



It would seem from Mr. Prestwich' s observations that the small patch of carboniferous sandstone and shale 

 with a thin seam or two of impure coal which occur at Shirlot on the southern edge of Willey Park, sur- 

 rounded by and reposing on the Old Red Sandstone, does not belong to the upper but to the lower coal 

 measures. The sandstone on which Shirlot monument is built is a good example of the lithological structure 

 of many of the lower coal rocks. 



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