Yol. 6o.l TWO DEEP BORINGS AT CALVERT STATION". 341 



Discussion. 



The Secretary read the following letter, received from Mr. S„ 

 S. Bucioiajnt: — 



' The discovery that at Calvert the ornatum zone rests directly upon Forest 

 Marble is very interesting, because immediately south of Calvert the road to 

 Edgcot passes over a knoll of Cornbrash, which forms a conspicuous feature 

 with a steep hill overlooking the village of Edgcot. There must be a con- 

 siderable area of Cornbrash here, and the characteristic rock with brachiopods 

 is exposed by the roadside north of Edgcot ; but this inlier of Cornbrash is not 

 marked on the Geological Survey map. It is the eastern extension of the line 

 of inliers of Cornbrash which extends from Islip to Ainbrosden and to Marsh 

 Gibbon. 



'The Cornbrash of Edgcot must be about 100 feet above the base of the 

 Omatus Clays of Calvert, and so there must be a fault to that extent just south 

 of Calvert Station. 



' It is interesting to note that beds missing on the downthrow side of a fault 

 are preserved on the upthrow side. The case is exactly parallel witli that of 

 the Peak Fault in Yorkshire. The explanation would seem to be that the 

 original axis of the anticlines lay to the north, and that the denudation of the 

 anticlinal folds— in the Calvert case pve-ornatum, in the Peak case pre- 

 murcliisoncB — was accomplished long before the present fault-lines were 

 developed.' 



Mr. G. Barrow drew attention to the persistence of the bright 

 green clays in the Forest Marble Group, and asked whether the 

 Authors had ascertained if these clays had been met with in the 

 deep borings under London. 



Mr. L. J. Wills enquired of the Authors the distance between 

 the two boreholes, in view of its bearing on the possibility of the 

 occurrence of Trias, as suggested by them, in the western one. 



Dr. J. Y. Elsden commented upon the description of the absence 

 of Kellaways Bock and Cornbrash in the borehole as a non- 

 sequence, and asked what this term implied. Did it mean non- 

 deposition, contemporaneous erosion, overlap, or what '? "With 

 regard to the Bletchley Boring, the speaker believed that Charnian 

 rocks occurred here immediately below the Mesozoic, the thick 

 Shineton Shales shown at Calvert being apparently absent, and 

 he asked whether the paper threw any light upon this question. 



Dr. C. A. Matley alluded to the great interest of the discovery 

 of Cambrian rocks in the boring, and the close lithological resem- 

 blance of these Tremadoc shales with those of Shineton, Malvern, 

 and Merivale. The compound oolitic grains in the Jurassic lime- 

 stones shown in the lantern -slides exhibited, reminded him of those 

 from the (pre-Cambrian) Cemaes limestones of Anglesey, described 

 and figured by the late J. F. Blake in the British Association 

 Beport for 1888. They seemed to the speaker to yield no proof of 

 contemporaneous erosion, but to be recently-formed grains which 

 had become agglutinated as they were moved about by marine 

 currents, and then, coated by further layers of carbonate of lime. 



Mr. W. H. Booth asked whether the Authors had obtained any 



