﻿Vol. 6 I.] SEQUENCE IN THE BRISTOL AREA. 195 



compact in texture, with good coiichoidal fracture ; others 

 are granular and encrinital, 



Eormer designation: 



(3) Middle Shales (upper part only). 



(4) Mitcheldeania-Be&s, at the base of the Middle Limestones. 



Where exposed in the Avon section : — 



Clifton side : The upper part of the cutting between the Gully 



Oolite-Quarry and the Great Quarry, and the lower third of 



the Great Quarry. 

 Leigh "Woods side : The lowest beds in Quarry 4 (see 



PI. XXVII). 



Special faunal characters : — 

 Brachiopods : 



Seminula ficoidea and its allies become extremely abundant,, 

 and are associated with prolific specimens of a giganteid Productus 

 (Pr. 0). 



Productus semireticulatus still occurs, and a well-marked muta- 

 tion with very long spines characterizes a bed at the top of the 

 subzone (the so-called ' longispinus '-bed). 



Productus aff. 7iemisp7iericus is not uncommon. 



Syringothyris aff. laminosa and Athyris (?) sp. occur in con- 

 siderable numbers at one level. 



Orthotetes crenistria, in a characteristic mutation, is found 

 somewhat rarely in the upper beds, and the gens has entirely 

 lost that predominance which is so noteworthy a feature of the 

 Tournaisian facies. 



Corals: 



Caninia cylindrica (especially in its mutation bristolensis) is 

 abundant chiefly in the upper half, and with it are associated 

 (probably) occasional specimens of Amplecvus and Michelinia. 



Syringopora becomes common at the top in a distinct form 

 (cf. S. distans). 



Lithostrotion Martini appears early in the subzone, and, in the 

 upper portion, whole beds are made up of this species and of one 

 of its varieties. 



Lithostrotion basaltiforme (var. bristolense) has long been known 

 to collectors ; it abounds in a few beds near the top of the sub- 

 zone (one of these beds, which is stained black hy petroleum, is 

 known as the ' A7*anea-Be& '). 



Alveolites sp. and Cyathophyllum are rare. 

 A characteristic bryozoan in this subzone is Heterotrypa tumida. 



S 2 = Subzone of Productus Cora, mut. S 2 . (The main 

 portion of the Seminula-Zone.) 



Lithological character. — Chiefly massive limestones, containing 

 a thick series of oolites near the base, and concretionary limestones 

 (with shale-partings) at the top. 



