THE RH^TIC ROCKS OF PYLLE HILL, BRISTOL. 221 



iferous, whereas with the very coinniencement of the Avicula 

 contorta shales we get evidence of the incoming of a decid- 

 edly marine fauna, including not only forms of life that 

 characterize the Rheetic formation of Europe, but also species 

 of mollusca and reptilia which range into the overlying 

 Liassic strata. For these reasons, then, I am of opinion that 

 in Notts and the adjacent counties at any I'ate, the line 

 between the Rhestics and the Trias should be drawn at the 

 base, not of the green marls, but of the Avicula contorta 

 beds." And again : " Probably in both districts " (i.e., in 

 Notts and the West of England) " these green marls were 

 once red in colour" (as is evidenced by the occasional pre- 

 sence in them of red blotches) " and non-calcareous, and 

 have since become bleached and calcareous in part by the 

 downward infiltration into them of some deoxidizing chem- 

 ical agent and carbonate of lime, derived from the decom- 

 position of the abundant organic remains of the overlying 

 Avicula contorta shales. The very general occurrence of 20 

 feet or so of " greenish marls ' at the top of the Keuper Marls 

 in this country is a coincidental result of discoloration. 

 Neither the textural characters, the stratigraphical relations, 

 nor the organic remains of these beds, justify us in separating 

 them from the rest of the Keuper formation and classing 

 them as R-hastic." * In my later paper on the Pylle Hill 

 section, I observed also on the difficulty there was in sup- 

 posing these " Tea-green Marls " could be a " passage-series " 

 from Keuper to Rhgetic, owing to" the fact that they form a 

 natural capping to the Upper Keuper Marls in different dis- 

 tricts, where that series attains very different dimensions 

 and therefore cannot be on the same horizon in all cases. I 

 also noticed the fact, which I would emphasize here, that 

 except for a faint resemblance in colour, the mineral char- 

 * Quart. Journ. Geol. Soc, vol. xxxviii. p. 451. 



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