Yol. 51.] OF THE MID-COTTESWOLDS. 431 



Table VI. (plain lines) shows a rapid rise in the thickness of the 

 ' intervening beds ' from Mount Surat to Stroud Hill. The thickness 

 is maintained to Sheepscombe, and then a decline commences, which 

 becomes very rapid between Buckholt and Cranham Woods. Next, 

 after passing Birdlip, there is a rapid rise, the line for which travels 

 nearly straight from Tuffley's to Ravensgate, the only deviation from 

 straightness, it may be noticed, coinciding with a change of direction 

 from about N.E. to E. 



The important point for remark in Table YI. is what I may 

 perhaps call ' the trough,' which has been cut through the ' inter- 

 vening beds ' in the neighbourhood of Birdlip by the Bajocian 

 erosion. It will be seen that on each side of this trough, wbich 

 is, of course, much exaggerated by the difference in the hori- 

 zontal and vertical scales, the formations do not thin out ; but that, 

 as the ' intervening beds ' increase in thickness, a higher formation 

 is always brought in. Again, it will be observed that on each 

 side of this trough the beds, when met with, stand at practically the 

 same levels. Now these observations are important, because they 

 prove that the trough is one of erosion, and is not due to any 

 thinning out, or non-deposition of the beds at the time over the 

 Birdlip area. Had the trough been due to the latter cause, a thin- 

 ning of all the ' intervening beds ' on each side of the trough would 

 have been observable ; and it would not have been the case that the 

 uppermost of the ' intervening beds ' was always absent where the 

 thickness was less : on the contrary, all of the ' intervening beds ' 

 ought to be found, but each one of diminished thickness, or, if any 

 were missing, the under and the middle beds would have just as much 

 chance of being absent as the top one. Now it is seen that these 

 conditions are not fulfilled, and that in each case upper beds do not 

 make their appearance unless the full sequence of their predecessors 

 have been completed. 



It is therefore reasonable to conclude, and the diagram illustrates 

 this assumption, that all the formations mentioned, the Notgrove 

 Freestone, Gryphite-grit, etc., were at one time continuous from 

 Cold Comfort and Leckhampton to Kimsbury Castle and beyond ; 

 and that at Leckhampton and Kimsbury Castle, and over the inter- 

 vening area, the Notgrove Freestone was of fair thickness, say 10 

 to 12 feet. It is also very probable that the Witchelli a-grit ex- 

 tended over this same district. Perhaps, too, there were beds of 

 later date than the Witchellia-grit, yet earlier than the Upper 

 Trigonia-gvit, but they were completely denuded. The Witchellia- 

 grit has been preserved over only a very small extent of country — 

 what with erosion before the deposition of the Upper Trigonia-grit, 1 

 and the much greater erosion of more recent date, it has been left 

 over an area of only 1| square miles ; so it very nearly happened 

 that the W itchellia-giit vvas altogether lost. What came about so 



1 This Bajocian erosion was quite unexpected, and it is different from what I 

 have surmised elsewhere ; but there must, of course, have been areas of non- 

 deposition, only more to the south-east: ' The Relations of Dundry with the 

 Dorset^Somerset and Cotteswold Areas during part of the Jurassic Period,' 

 Proc. Cottesw. Nat. Field-Club, vol. ix. (1889) p. 383. 



Q. J. G. S. No. 203. 2 h 



