460 PKOCEEDIKGS OF THE GEOLOGICAL SOCIE'ir. 



differences when varions sections of these beds are compared, still 

 their persistency over a wide area in the South-west of England is 

 remarkable ; and though the Lias above and the Keuper marls be- 

 neath, particularly within the Coal-basin, are repeatedly found 

 unconformable from the absence of some of their members, the 

 Ehsetic beds are always present. 



In a former paper I gave the Beer Crowcombe sections, and 

 others near Langport, as typical, and these may still be considered 

 correct ; but I was under the disadvantage of having to trace the 

 succession of beds in several quarries. I propose now to give an 

 important section in the i-ailway-cutting at Queen Camel, in which 

 there is a succession of 260 beds, having a thickness of 375 feet, 

 every one of which may be studied, and where at one view is seen 

 the passage upwards of the Keuper, Ehsetic, and Liassic beds. The 

 passage between Rhaetic and Lias beds seems here less broken than in 

 many other sections ; but, in this case as in every other, the peculiar 

 lithological distinction in the two deposits can be immediately recog- 

 nized, and you may at once place your hand upon the uppermost 

 Ehaetic " Sun Bed." This distinction is generally so strongly marked 

 that any geologist, even if travelling by express train, may rea- 

 dily detect the junction of the Ehaetic with the Liassic beds in the 

 railway-cutting at Saltford, near Bath. The "■ "White Lias " extends 

 uninterruptedly from Lyme Eegis through Somersetshire, however 

 unconformable may be the beds immediately resting upon it ; but it 

 thins out or entirely disappears in North Gloucestershire and beyond ; 

 and it is noteworthy that continental geologists have not yet recog- 

 nized its presence in any of their sections*. 



The Ehsetic beds appear to have been deposited under peculiar 

 oceanic conditions, and in general must have been accumulated very 

 slowly. The blue marls of the Avicula-contorta series at their base 

 are usually most persistent, and are crowded with testacea. But at 

 times the Bone-bed is entirely absent as a separate zone ; and the 

 vertebrate remains it yields are then either distributed throughout 

 the other beds, or are found in little nests or pockets therein. The 

 Aust section affords the best horizontal illustration of the Bone-bed, 

 which is there a nodular stone of some thickness, the accumulation 

 of which indicates a period of rest, or a lapse of time within which 

 the organisms it encloses must have been living. Again, the Avicula- 

 contorta limestone, or the " Plinty Bed " of my Beer Crowcombe sec- 



* Since the above remark was made, I have seen M. Jules Martin's " Paleon- 

 tologie Stratigraphique de I'lnfralias," in which he remarks that M. Eug. 

 Dumortier had found in the Departments of the Rhone and Ardeche, between 

 the Gryphsea-limestone and the Trias, two distinct mineralogical zones, the upper 

 composed of a whitish limestone with grains of clear quartz with Cardinice and, 

 lower down, Littorina clathrata, Desh. The lower zone, he remarks, is composed 

 of compact limestones in a very fine paste, almost " lithographique," of a clear grey 

 tint, and often presents a multitude of round holes, which M. Leymerie attributes 

 to perforating shells, these being known under these name of the choin hdtard; and 

 he adds that they represent the common zone of Littorina clathrata. This de- 

 scription so completely accords with the lithological character of the Rhsetic 

 ' ' White Lias " that I can readily suppose they are identical, in which case the 

 Rhgetic Avicula-contorta beds would probably be found immediately below. 



