220 PKOr. S. H. KETIN-OI.DS ox THE LITHOLOGICAL [vol. Ixxvii, 



There are no exposures of this horizon in the rail way- cutting on 

 the left bank. 



[4^) K.,. (Thickness=about 285 feet.) — The lower K, beds are 

 not exposed on the right bank of the Avon, being overgrown or 

 hidden hy walls. The middle beds are poorly seen in the railway- 

 cutting. The upper beds are better exposed in Press's Quarry ^ 

 (where about 30 feet are seen) and in the adjacent railway-bank. 

 The middle beds consist of highly fossiliferons, thinly-bedded, 

 crinoidal limestone and shale, the shale (which is sometimes gritty) 

 predominating. Ostracods and bryozoa are plentiful, but the 

 prevalent limestone-builders are crinoids and brachiopods. 



The upper beds consist of highly crinoidal and brachiopodal 

 limestone, with thin shaly partings. The matrix between the 

 crinoidal ossicles is sometimes partly dolomitized (A 38), but 

 dolomitization is by no means especially characteristic of this 

 horizon. On the other hand, many of the fossils are silicified. 

 Miss Chapman's analyses, ^ three in number, show the presence of 

 magnesia varying in amount from 6 07 to 7'42 per cent. 



On the left bank of the Avon a cutting in the woods just north 

 of the northernmost quarry (Quarry 1) gives a good section of some 

 35 feet of the upper beds. The rocks consist of highly fossiliferous 

 limestone interbedded with shale. Nothing is seen of the middle 

 or lower part of K.^ on the left bank of the Avon, and the horizon, 

 as a whole, is worse exposed in the Avon Section than any other. 



(B) The Zaplirentis Beds. (Thickness, including 

 Horizons (3 and 7 — about 396 feet.) 



[The lithological succession is in close agreement with that of 

 Grower.] 



(1) Horizon /3. (Thickness = about 20 feet.) — The lowest 

 20 feet of rock exposed in Press's Quarry, at the base of the 

 precipice below Sea- Walls, are assigned to this horizon, but without 

 definite palaeontological evidence to separate it from Z^. It consists 

 mainly of thickly-bedded massive limestone crowded with crinoids 

 and brachiopods, and with bryozoa not infrequent. Miss Chapman 

 records 9 "99 per cent, of magnesia in a rock from Horizon ft, but 

 I have not observed any highly dolomitized band. Possibly her 

 specimen came from a band which I regard as belonging to the 

 base of Z^. As in K^, there is some silicification of the fossils. 

 A thrust-fault traverses the cliff overlooking Press's Quany. 

 Near the top of the cliff it runs parallel to the bedding-planes ; 

 but, as it passes down, it begins to cut across them, until at the 

 base of the cliff it is inclined to thera at an angle of about 35°. 



^ Press's Quarry is a small quarry continuing Black "Rock Quarry to the 

 north. 



- Geol. Mag. 1912, p. 499. 



