246 C. E, De Ranee — Deposition of Cretaceous Strata. 



EXPLANATION OF PLATE XIL 



Fig. 1 . Gycloptychius carbonarius, Huxley ; caudal region imperfect. Nat. size. 



2. Another specimen, shewing the hinder part of the body with perfect tail. 



Natural size. 



3. Sketch of the side of the head with the bones of the face and shoulder. 



Somewhat enlarged and restored. 

 op. operculum ; p. op. preoperculum ; s. op. suboperculum ; ». o. sub- 

 orbital ; mx. maxillary; mn. lower jaw, hm. hyomandibular ; br. 

 branchiostegal rays. 1st s. cl. first supra-clavicular ; 2nd s. cl. second 

 supra-claYicular :; cl. clavicle ; p. cl. post-clavicular ; i. cl. iuter- 

 clavicular. 



4. Hyomandibular bone, enlarged. 



5. Magnified view of the ornament of the scales of the flank, from the speci- 



men represented in Fig, 1 . 



6. Outline of an isolated scale, magnified, from a specimen in which the scales 



were disjointed. 



II. — On the Physical Changes preceding the Deposition of the 

 Cketaceous Strata in the South-west of England.^ 



By C. E. De Eance, F.G.S., of the Geological Survey of England and "Wales. 



Zone of Scnphites cequalis. — Beneath the Yellow Chalk of West 

 Dorset and South Somerset occurs a very constant bed of yellow 

 calcareous paste, with glauconitic grains, and containing at the base 

 numerous small minute pebbles of quartz, the whole being so well 

 cemented together as to be used at Pennys Toller, near Bea- 

 minster, as a rough building stone. In 1865 I collected from this 

 zone a large number of fossils, most of which I found to occur in the 

 Cambridgeshire " Chloritic marl," Chardstock, Buckram, and Pennys 

 Toller being perhaps the most fossiliferous localities. At the base 

 occurs a well-marked horizon of Ammonites Khotliomagensis. 



Zone qfPecten asper. — A bed of dark brown-coloured quartzose sand- 

 stone, 20 feet thick, sometimes forms the top of the Upper Greensand. 

 It is well seen at Seamark Hill, where it contains Exogyra conica, 

 and at Tytherleigh. Eastwards, from Seamark to Buckram, it thins 

 out, and overlies and is partly equivalent to a bed of light-green 

 coarse-grained sandstone, about 16 feet in thickness, in which the 

 Fectens occur. This portion of the bed is very constant, being seen 

 in most of the sections on the top of the Oolitic hills from Chard 

 in Somerset to Eggardon Hill in Dorset — a range of country more 

 than twenty-five miles in length. 



Zone of Exogyra co?i«ca.-^These beds consist of very soft bright 

 yellow (occasionally pale green-coloured) sand, with vast numbers 

 of Exogyrce, often of very large size. Both the two last-mentioned 

 zones are present at Blackdown. It is generally about 15 feet thick, 

 and is usually present in all the Lower Cretaceous sections of East 

 Devon, South-west Somerset, and West Dorset. 



Fox Mould. — The deposit locally known by this name consists of 

 loamy sand. At Pinhay it reaches a thickness of 60 feet, and is 

 nearly as thick at Black Ven, where it overlies the Cow Stones. In 

 the latter locality it forms a loose shifting mass, through which the 

 cutting of the Lyme Eegis road has been carried, and has been the 



^ The publication of this paper has been unavoidably postponed. — Ed. Geol. Mag. 



