338 ME. T. F. SIJ3LY ON THE CARBONIFEROUS [May I906, 



removal of the covering of Triassic and Jurassic deposits. In the 

 southern part of the area, the Dibunopliyllum-ZonQ has a very 

 small outcrop, and is exposed only at two or three points. East 

 of Downside, as far as Heale, the northward extension of the Lias 

 and Inferior Oolite is so great, that the outcrop of the Avonian 

 rocks is intermittent, and is confined to the Cleistopora- and 

 Zaphrentis -Zones. The Heale fault, by letting down the Limestone 

 on the east, brings in the Dibunojihyllum-Zoue at Leighton, where 

 the overlying Inferior Oolite has been removed ; but, in the extreme 

 east of the area, the Carboniferous Limestone is exposed only in 

 the gorges of streams, which have cut through the superincumbent 

 Oolites, as at Yallis Vale, Whatley Bottom, and Holwell Valley. 



IV. Description of Exposures in the Mendip Area. 



(i) Continuous Sections. 



Only four sections in the Mendip area can be classed as 

 continuous sections.' 



(a) The Burrington-Combe section, on the north side of the 



Black-Down pericline. 



In Proc. Bristol Nat. Soc. ser. 4, toI. i, pt. 1, 1905 (issued for 1904), 

 pp. 14-41, I have described this fine section, which affords by far the 

 most complete sequence exposed in the Mendip area, in detail ; con- 

 sequently, I need only here mention its extent. 



Zonal extent : — All the zones and subzones up to, and including, the 

 base of the Dibunophy Hum-Zone. 



(b) The Cheddar-Gorge section, on the south side of the Black- 



Down pericline. 



This magnificent gorge, together with the ravine which, branching off 

 on the east side, runs northward to Long Wood, affords a fine section. 



Zonal extent: — Upper Syrinyothyris-Zone, Seminula-Zone, and the 

 base of the Dibunophyllum-Zone. 



(c) The Maesbury rail way- section, on the north-western side of 



the Beacon-Hill pericline. 



The cutting on the Somerset & Dorset Joint Eailway, north of 

 Masbury 1 Station, affords the only really good section of the Cleisiopora- 

 Zone to be found in the Mendip area. 



Zonal extent: — Clcistopora-Zone (K v K 2 , & (3) exclusive of the 

 lowest part (M). 



(d) The Vallis-Vale section, near Frome, on the north side of the 

 Beacon-Hill pericline. 



The numerous quarries in Vallis Vale, taken together, constitute a 

 fairly-continuous section. 



Zonal extent : — Upper Zaplirentis-Zone (Horizon 7 not exposed), 

 Syrinyothyris-Zone (uppermost 400 feet exposed), and the base of* the 

 Seminula-Zone. 



1 Misspelt thus by the railway-authorities. 



