432 J. Prestwich, Esq., on the 



lengthened description. The vertical scale is necessarily much exaggerated in order to show each 

 stratum, and to avoid too great an extension. The changes in lithological characters also are 

 partially illustrated in the same diagram. 



It may be mentioned that rapid changes in thickness and composition are generally concomi- 

 tants. The upper and lower clunches of the northern and central districts pass, as they ex- 

 pand* in their range southward, into hard shales, and eventually into sandstones, with a few 

 subordinate beds of shale. The strata of sandstones, marls, clays, and shales, indeed rarely 

 maintain the same appearance for a mile, and frequently differ considerably in the space of 

 twenty yards. The shales are however far more constant in composition than the sandstones, 

 which vary incessantly, passing from a fine-grained into a very coarse rock or into a more or 

 less compact shale. For example, the best coal rock at the Meadow Madeley pits changes from a 

 light buff-coloured sandstone into a hard dark gray shale. At Ketley, the sandstone over- 

 lying the Penneystone is of a bright ochreous colour, and at Broseley it is quite white. The cu- 

 rious phenomenon locally called " Symon fault " is another instance in point. This apparent 

 fault is occasioned by the gradual, but complete substitution of the coal by clay, shale, or sand- 

 stone. The coal is at first deteriorated by a slight admixture of one of these substances, the pro- 

 portion of which rapidly increases, until it entirely replaces the coal. This phenomenon is of 

 common occurrence in the neighbourhood of Broseley and Caughley, and occasionally at Madeley 

 and Priorslee. The alteration in the coal varies in extent from ten to five hundred yards. At 

 Langley, a sandy " Symon fault" occurs in the Penneystone measure, when a great increase in the 

 number and variety of the organic remains was observable. Another great change in lithological 

 characters, and in the thickness of the strata, occurs between Lightmoor and Madeley. In all the 

 series above the flint coal it is difficult to trace the connexion between the two districts. (See Dia- 

 gram.) Notwithstanding these frequent changes, the coal-measures, as mentioned at the commence- 

 ment of the chapter, preserve a certain general arrangement. 



A very important example of this phenomenon is exhibited at Malinslee. 

 The upper strata are the first affected, but the altered structure gradually per- 

 vades the whole of the measures, as they trend eastward. The change is 

 apparently produced by an admixture of red and yellow clay, marl and sand, 

 locally called " Calaminker". The upper coals and ironstones are replaced by 

 beds of this character immediately east of Malinslee, the change in the flint coal 

 shortly follows, then the gray and uniformly thick Penneystone stratum assumes 

 the appearance of a mottled red shale, and finally the clod and lower coals 

 vanish at Randley Wood, half a mile east of where the change commences in 

 the upper strata. A somewhat similar and equally remarkable alteration oc- 

 curs in the northern extremity of the field, commencing between Donnington 

 and Munton. The upper strata there pass into thick irregular beds of concre- 

 tionary red and light greenish conglomerate, containing a few very thin lay- 

 ers of coal, and some subordinate beds of shale. The deeper strata are how- 

 ever less affected, and at a trial pit sunk near Lilleshall Hall, the strata from the 

 clod coal up to the top of the flint rock above the Penneystone, corresponded 



* Excepting in their temporary expansion at Ketley and Arleston. 



