THE GEOLOGY OP TYTHERINGTON AND GEOVESEND. 13 



Shales. The subjoined table gives my own classification of 

 the series in the Avon section. The estimated thicknesses 

 are given in round numbers. I place the line of division 

 between the Upper Transition Beds and the Upper Lime- 

 stone at a point 340 feet on the Bristol side of where the 

 new zigzag path crosses the rail. The points at which the 

 boundaries of the strata cross the Port and Pier railway 

 were determined on the six-inch Survey map. Through 

 these points lines of strike were laid down ; the strata 

 were measured across the outcrop at right angles to the 

 line of strike ; and the thicknesses calculated for a mean 

 dip of 27|°. 



The Avon Section at Clifton. 



Feet. 



Upper Transition Beds (Upper Limestone Shales) . . 400 



Upper or Lithostrotion Limestone 800 



Middle Transition Beds {Mitc'heldeania-'hedi'&) . . . 200 



. ., ,T. , C The Gully Oolite, 100 feet ) ^^^ 

 Lower or Encnmtal Limestone < _, _, ^ „ ^ .^-.^ i. . C "^^ 



(. The Black Kocli, ooO feet J 



Lower Transition Beds (Lower Limestone Shales) . . 320 



Total .... 2370 



In the Tytherington section the continuity of the beds is 

 broken by the reversed fault. There can be no doubt, how- 

 ever, that the beds in Mr. Hardwicke's quarry belong to 

 the Upper or Lithostrotion Limestone. The bituminous 

 beds on either side of the so-called " Fire-stone " may very 

 possibly be equivalent to the similarly bituminous beds of 

 the Grreat Quarry of the Avon section. But I know of no 

 " Pire-stone " in that quarry. 



The thin-bedded argillaceous limestones which come in 

 beneath the Trias in Sub-section 3 are, I take it, near the 

 top of the Middle Transition {Mitcheldeania) Beds. The 

 Grully Oolite is well represented just beyond the Tythering- 

 ton tunnel, and is followed by the Black Rock limestones. 



