188 MR. A. RENDLE SHORT ON RUSTIC [May I904, 



have since been decided on, seeing how well the Jurassic has been 

 zoned. I would suggest the following : — 



( Planorbis-Zone. ) 



n7 „ 7 . r, 1 [ Some beds of Blue Lias. \ 



Pleuromya-Croivcombeia Zone. ( = \ W i .. T - ) 



Monotis-deciissata Zone. ' ( — Cotham Marble and just above). 



Naiadita and Estheria-mimvta, } , ,r . ,., •„ ■, , 

 t, 7- „ - ( = J\ a tad it a- Beds). 



var. Brodieana-Zoue. J v 



Pecten-valoniensis Zone. ( = Pecten-Beds). 



Avicula-contorta Zone. ( = Black Shales). 



Bone-Bed. 



(Keuper.) 



Pecten valoniensis is recorded in the Black Shales, and also in the 

 White Lias. Except those specimens that occur just at the top of 

 the Black Shales, however, I believe that nearly all the former are 

 really Gardium cloacinam, which has but lately been recognized in 

 England by Mr. L. Richardson and Mr, A. Vaughan ; and most, if 

 not all, the White-Lias forms are probably Pecten dispar (Terquem), 

 which, however, is not very different (Vaughan). 



Naiadita was originally described by Buckman and Brodie as 

 occurring above the Cotham Marble at Aust, Horfield, etc. In 

 all the places that they mention it certainly occurs below, and 

 never (to my knowledge) above the Cotham Marble. All later 

 writers agree in this. 



Pleuromya Crowcombeia is not the same as Pttromya Crowcombeia 

 (which is a fossil from the P^<?n-Beds). It is very common in 

 the White Lias and in the lowest beds of the Blue Lias, and 

 appears to be recorded under the most various names. It becomes 

 extremely rare when the ammonites begin. 



The ranges of Gardium rhceticum, Modiola minima, and Ostrea 

 liassica are too long to allow of their being used for zoning. The 

 saurians are inconstant. 



It is not contended that the zone-fossils are confined to their 

 own horizon : for example, Monotis decussata is occasionally found 

 in the Lias ; but they are only met with in any abundance there, 

 and are of very practical service. 



(i) With regard to the constancy of these zones throughout 

 England, I would submit that they are fairly constant, and would 

 especially refer to the four sections described in this paper, and to 

 Garden Cliff (54), Wainlode (54), Wood Norton near Evesham (51), 

 Stratford-on-Avon (2, 20), Watchet (6) : here Pecten valoniensis is 

 recorded below the Bone-Bed — this is unique, and there appears to 

 be doubt about it, for Etheridge, whose determination it was, 

 afterwards marks it with a query (17), Camel Hill (13), Notting- 

 ham (31), Pylle Hill (36), and Penarth (17). The other sections 

 are less perfect, but there are no difficulties that a fresh search 

 would not probably remove, as indeed has happened at Garden Cliff, 

 where Mr. Richardson's observations bring it better into line than did 



