﻿214 DE. A. VAUGHAN ON THE PALjEONTOLOGICAL [May 1905, 



fossiliferous equivalent of part of the unproductive Middle Shales 

 and Dolomites of the Avon section. 

 Quarries in the Seminula-Zone : — 



(1) At the corner where the Clifton road branches off, immediately- 



west of Longwood House, is a small quarry containing 

 Semimda in abundance and traces of Productus, but no 

 Lithostrotion. This quarry lies due south of the small oolite- 

 quarry north of Wraxall Piece, and the strike is again 

 almost due east and west. 



Calculation from the map proves that the beds here are 

 about 350 feet normally above the base of the Oaninia- 

 Oolite; hence, assuming the general thickness of the Caninia- 

 Series to be the same here as in the Avon section, this 

 quarry should represent the very lowest beds of the Great 

 Quarry. 



(2) The large lime-quarry in the Seminula-Oolite lies 900 yards 



east of Longwood House, at the side of the Clevedon road ; 

 a rough calculation from the map makes the beds in this 

 quarry about 300 feet normally above those of the last 

 quarry, and this accords well with the position of similar 

 beds in the Avon section. 



The other exposures mentioned below can only be referred to 

 their correct stratigraphical position by the fossils found in them, 

 since they lie isolated in those parts of the area where both strike 

 and dip undergo rapid variation. Consequently, the results deduced 

 from such exposures do not help to determine the zonal sequence, 

 except in so far as they demonstrate the constant co-occurrence 

 of the same forms. 



Detailed Description of Zones. 

 Tournaisian. 



Modiola-Zone (M). 



Lithological character. — Shales with thin limestones, capped 

 by a thicker band of red limestones (Horizon a). 



Exposure. — In the Failand section, near Millpond Farm. 



Fauna. — An ostracocl (? Leper ditia), identical apparently with 

 the one which is very common in the Avon section, is 

 extremely abundant in one of the limestone-beds below 

 Horizon a. 



At Horizon a the red limestone is crowded with crinoidal 

 debris. JRhabdomeson is abundant, and palatal teeth are not 

 uncommon. 



Cleistopora-Zone (K) and Horizon /3. 



Lithological character. — Shales with beds of limestone, 

 the limestone predominating at the top. 



