452 



COAL MEASURES AND CARBONIFEROUS LIMESTONE. 



Coal Measures and Millstone Grit. 



On these formations it is unnecessary to dwell, as they occupy so small a portion of the annexed 

 map and have been fully described by other authors. The same two beds of coal mentioned by 

 Mr. Weaver are still wrought at Cromhall Heath, though further upon the dip, and consequently 

 at greater depths. It is, however, desirable to point attention to the underlying strata of grit and 

 shale with courses of impure limestone, which support this coal-field, because they resemble beds of 

 similar age at Oswestry (p. 144). The general colour of these underlying and unproductive coal 

 measures is red, a colour which prevails in rocks of this age at Oswestry, Lilleshall, &c. As we 

 proceed we shall point out, that this colour also characterizes the surface of two-thirds of the rock 

 formations of the Tortworth district. Messrs. Buckland and Conybeare have considered all these 

 red and white grits, with courses of red shale and impure limestone, as equivalents of the upper 

 limestone shale beneath the millstone grit. Besides, however, the true upper limestone shale of 

 these authors, a detailed section of which, by Mr. Lonsdale, is given (p. 158), there are at Cromhall 

 quartzose conglomerates and reddish grits, which as they immediately pass under the coal-bearing 

 strata and overlie the calcareous formation, may be grouped with the millstone grit. (PI. 36. f. 21.) 



Carboniferous or Mountain Limestone. 



To the south of Tortworth, this formation is thrown up in a horse- shoe outline, rising from be- 

 neath the millstone grit and coal measures of Cromhall into rocky masses, for the most part well 

 wooded. It is unnecessary to describe this well-known limestone, or to say that it is in many parts 

 charged with its usual organic remains. The dislocations, however, to which it has been subjected 

 are worthy of notice. So far from presenting an uniform and unbroken band, as might be supposed 

 from its appearance when laid down upon a small scale, it is broken into a number of distinct 

 masses by transverse dislocations, which have the strata in each mass often dipping at different 

 angles and frequently in opposite directions ; such phenomena are observable along the ridge from 

 Tortworth Lodge to Tytherington : and in the rocky grounds south of Cromhall Park, the limestone 

 is so dislocated as to form sometimes double troughs dipping E.S.E. and W.N.W. at angles of 35° 

 and 40°, while near Tytherington it rises like a wall from beneath the Cromhall coal-field. In this 

 range, its upper part contains a subordinate band of reddish sandstone, the firestone of the country 

 people. In the map a considerable extension is given to the limestone south-west of the Tortworth 

 and Cromhall tract. At Littleton -on-Severn, where it is the fundamental rock on which the do- 

 lomitic conglomerate, New Red Sandstone, and lias repose, the limestone becomes very sandy, 

 passing into chert, and sometimes weathering to a yellow colour, with druses containing decomposed 

 magnesian limestone. There can be little doubt that much of the adjacent dolomitic conglomerate, 

 which in its aspect and matrix so much resembles this limestone, has been derived from this source. 

 The prevailing fossils at Littleton are Encrinites, and the Spirifer trigonalis (Sow.). 



Besides the ordinary characters and prevailing fossils of the carboniferous limestone 

 with which this tract abounds, it also presents certain beds of transition between the 

 limestone and the Old Red Sandstone, (the lower limestone shale of Buckland and 

 Conybeare,) to which special attention must be paid, since they so much resemble 



