238 Corresjmidence — Mr. H. H. Winicood. 



coiaii:His:F'on^X)iiiniTCE. 



♦ 



THE MILLSTONE GEIT AT VOBSTER. 



SiR^ — The amount of disturbance and confusion existing in 

 the Coal-measures immediately north of the Mendip Hills has long 

 been a subject which has greatly exercised the scientific imagination 

 of geologists. Any fact that can throw light upon the question, or 

 that serves to support one theory or the other in explanation of the 

 inversions of strata in the Nettlebridge Valley, is worthy of record. 

 One such fact it is in my power to lay before your readei'S in con- 

 nexion with the Vobster inversion. That coal has been worked 

 beneath this mass of limestone it is scarcely necessary for me here 

 to assert. Mr. McMurtrie lias satisfactorily established that fact in a 

 paper read before the Bath Field Club in the year 1874, and pub- 

 lished in the third vol. of the "Proceedings." But how did this mass 

 come here? In a paper contributed to your Magazine for 1871, 

 p. 150, with the legitimate horror entei'tained by a member of 

 H.M.G.S. against cataclysmic action, Mr. Horace B. Woodward 

 attempts to account for this abnormal position of the limestone by 

 a compound reversed fault and anticlinal theory, and an ingenious 

 " Diagram Section" is given to illustrate his view. In his dissent 

 from the theory which would account for this position by a folding 

 over of the main ridge, he states, that a serious difficulty presents 

 itself in the absence of the Millstone Grit which ought to be found 

 in its true position between the Mountain Limestone and the Coal- 

 measures proper, had their folding over to the north really occurred. 

 Now it gives me much pleasure to state that the discovery of 

 these hitherto missing beds in the position required must remove 

 this " serious difficulty." During a recent visit with Mr. McMurtrie 

 and others to Vobster, , we found that the quarry men, under Mr. 

 Batey's superintendence, in driving a tunnel through the south face 

 of the quarry in a northernly direction Avere then actually in the 

 Millstone Grit beds, which were severely trying the temper of their 

 tools. These beds dipped at an angle of about 46° S., and were 

 found beneath, shales and limestone dipping from 46"^ to 55° in the 

 same direction and thoroughly conformable. Thus another proof 

 has been added in support of the view that these beds have been 

 turned completely topsy-turvy ; in other words, the upthrow-fault 

 theory of the earlier writers having alread}' been proved to have no 

 real existence, and the chief objection which seems to have hindered 

 Mr. Woodward, a geologist well acquainted with our Mendip compli- 

 cations, from accepting the generally accepted view of a folding over 

 of the beds, having now been met ; what remains, but to accept 

 the alternative that these beds, originally horizcmtal, have been 

 squeezed together, thrown up, and finally folded over from the main 

 ridge, by some process which it would take a long glimpse down 

 the corridors of time to fully comprehend and unravel. 



11, Cavendish Crescent, Bath, H. H. WiNWOOD. 



