H. B. Woodward — Inversion of Coal Strata. 151 



which the Coal-strata present is such as to baffle description.^ From 

 Holcombe to Mells the beds are inverted, and dip to the south at 

 various angles, and he states that "at Nettlebridge every yard of 

 the ground has been jDroved, and the gradation traced from the point 

 at which the true northern inclination exists to where the abnormal 

 southern inclination shows itself." From this he infers that the 

 same disturbance which folded the Coal-measures back upon them- 

 selves carried with them masses of Limestone, of which the patches 

 in question are traces. 



He does not, however, attempt to explain this in the section he 

 gives, merely drawing a patch of Limestone resting unconformably 

 upon the inverted Coal-measures. 



In attempting to account for these vestiges of Limestone, two 

 theories suggest themselves. One, to which allusion has been made, 

 is that the Mendip anticlinal was so folded over to the north as to 

 bring the Mountain Limestone above the Coal-measures. But a 

 serious difficulty at once presents itself. What has become of the 

 Millstone Grit, which should occur between the two ? No trace of 

 this has been observed around any one of the three patches of Lime- 

 stone.^ The Grit is present in its regular position, but a mile off, 

 thoroughly conformable, as there is a gradual passage between it 

 and the Mountain Limestone below, and between it and the Coal- 

 measures above.^ The thought occurs that it might have thinned 

 out. That probably the area in which it was deposited was shallow- 

 ing, and that this is not to be accounted for by increase of sediment 

 alone, but must have been aided by elevation. That the elevation 

 being of unequal intensity over the whole area, the Mountain Lime- 

 stone might be raised above the sea-level in places, leaving the Grit 

 to be deposited in patches. Afterwards the Coal-measures would 

 entirely cover it, and overlap in places so as to rest directly upon 

 the Mountain Limestone.* 



But this is not a happy thought; there is no evidence whatever to 

 support a notion that any portion of the Mendip area was above 

 water whilst the Millstone Grit was in process of formation. 

 Again, the Millstone Grit near Coleford has been estimated (hy 

 Mr. McMurtrie) to have a thickness of 500 feet ; therefore, it could 

 not well have thinned out in so short a distance. And it is no 

 doubt persistent along the Mendip Hills, although the greater portion 

 of it is concealed by the Keuper Marls and Conglomerates. It is 



^ It has been remarked that the disturbances in the Somersetshire Coal-field 

 furnish " our nearest approach in Groat Britain to the abrupt foldings which are so 

 remarkable in the Coal-field of Belgium." (W. W. Smyth, etc.) 



2 And Mr. McMurtrie kindly informed me in a letter dated March 8th, 1870, that 

 so far as he was aware the Millstone Grit has never been detected between the Lime- 

 stone and the Coal-measures at Luckington and "Vobster. 



^ This gradual passage is clearly shown in Vertical Sections (sheets 11 and 12) 

 published by the Geological Survey of England. Indeed, it is well known that 

 from the Old Eed Sandstone to the Coal-measures in this area, there is no physical 

 break whatever. 



* On this subject, see also the remarks of Professor Ramsay, Mem. Geol. Survey, 

 vol. i., p. 312. 



