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band running through the shales. For distinctness' sake and on Palseon- 

 tological grounds I term these the Cardium shales, as the paper-like 

 laminae are literally foil of the compressed valves of Cardium lihceticum,, 

 associated, though spaiingly, with 



Pullastra arenicola, Strickl. 

 Pecten Yaloniensis, Defr. 

 Axiniis or Schizodus. 



In no part of the section do we ,find so many individuals of the species 

 of Ca/rdium Rhceticum as in these dark shales; and the physical characters 

 of these two series are sufficiently well marked to admit of my 

 describing them as two distinct beds. The dark Fissile beds 8 and 10, 

 divided by the Bone bed, if taken as one, would measure 9 feet 2 inches, 

 but physical conditions and organic contents require us to divide 

 them for intelligible reasons and easy recognition ; and the same 

 holds good on the ascending and succeeding shales, (No. 1 1 in section,) 

 which are dark gi'ey and marly, weathering into pale grey, and having 

 here and there intermittent thin bands of fine gi'ained Pyritic Sandstone. 

 (See section.) This series measures 2 feet 6 inches, and contains a large 

 number of the shell Avicula contorta, Portl., and I would name these 

 the Contorta shales, in conformity with naming No. 10 the Cardium 

 shales, for physically and Palseontologically they differ. In this group, 

 associated with A. contorta, occurs a small Axinus, and Cardium Rhceticum, 

 and a thin calcareous band, with fragments of Pecten Valoniensis, Defr. 



Capping these grey shales we have the true position of the Lower 

 Pecten bed, here represented by a thin, yet well-defined grey calcareo- 

 argillaceous drab-coloui-ed Limestone band, about 1 inch in thickness, 

 containing perfect shells and casts of Pecten Valoniensis. The position 

 of this apparently insignificant lamina at Westbuiy Cliff is on precisely 

 the same horizon as at Coombe Hill, Patchway, Aust Passage, and 

 Penarth, here characterised by an excess of lime in its composition; at 

 other sections it is mostly a Pyritic Limestone of extreme hardness. 

 This irregular line is marked a in the section between beds 11 and 12, 

 and which I make a distinguishing feature and line of demarcation 

 between the two beds of shale, as well as tending to fix or determine the 

 place of the two Pecteu beds, or the lower and upper, which here aa 

 elsewhere occur, but separated in the section by the shales No. 12, 2 feet 

 thick.* In these shales I failed to detect any fossils, although the 



* I know of no section in this group of deposits in the West of England in which 

 these two Pecten bands do not occur. 



