1820J Geological Societi/. [. 45I 



abundant in many of the shale beds : nodules of ironstone occur, 

 but in small quantity, and are not worked as ore in this field. 



The coal measures are often extremely convulsed; faults 

 which alter the level of the strata as much as 70 and 100 fathoms 

 in some places traverse them, and on the south, where the 

 lowest beds approach the inchned and nearly vertical calcareous 

 strata of mendip (their fundamental rock), they become broken 

 and contorted in a manner truly surprising ; the same bed of coal 

 being sometimes twisted into the form of the letter Z, and 

 pierced three times in the same perpendicular shaft ; near this 

 point also a series of coal beds becomes vertical, a pit being 

 sunk perpendicularly 80 fathoms in one individual seam ; and 

 the same series, when examined in different points along its line 

 of bearing, is found to change the direction of its dip on the 

 opposite sides of this vertical point in such a manner that the 

 beds which lie uppermost in the pits on the east of that point 

 are found (in consequence of this inverted dip) to occupy the 

 lowest place in those on the west. Many circumstances are 

 stated in the memoir as rendering it almost demonstrably certain 

 that the highly inclined position of the strata, and their remark- 

 able contortions, must be ascribed to mechanical violence which 

 has dislocated and elevated them subsequently to their consoli- 

 dation, and not to any circumstances of their original formation. 

 These arguments are strengthened by analogies derived from the 

 inclined strata of more recent formation in the Isle of Wight and 

 Dorsetshire, and shown to be apphcable also to the contorted 

 strata of transition and primitive districts. 



Inferences are hence drawn in favour of the elevation of many 

 of the principal mountain chains by forces acting on them 

 mechanically. 



This part of the paper is accompanied by an appendix con- 

 taining detailed lists of the strata sunk through in all the princi- 

 pal collieries ; many of these are very interesting, since from the 

 depth to which the coal measures are covered through extensive 

 portions of this field, by the more recent horizontal strata lying 

 unconformably over them, pits have in some places been com- 

 menced even in the lower beds of the great formation of calca- 

 reous oolite, and penetrated entirely through those of lias, and 

 of the newer red sandstone before reaching the coal. Thus the 

 history of those formations and their relations to the coal becomes 

 completely developed ; and since the connexions of the rocks 

 lying beneath the coal are exhibited with great distinctness in 

 other parts of this field, most of the obscure points in the history 

 of the rocks occurring in the neighbourhood of this important 

 formation will be found to receive a satisfactory elucidation from 

 the structure of this district, especially the distinction between 

 the formations so often confounded together of the older and 

 newer red sandstone. 



Having thus described the rocks of the coal formation, &c. aa 



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