218 THE RH-^TIC ROCKS OF PYLLE HILL, BRISTOL. 



One of the first things that strikes us in this Pjlle Hill 

 section — and it is a matter to be taken into account when 

 drawing any general deductions from same — is the very limi- 

 ted development of the Rhastic beds, the whole series, ac- 

 cording to my estimate, measuring only 17 feet in thickness. 

 This is not more than half the thickness these beds usually 

 attain in the West of England. At Westbury-on- Severn, for 

 instance, the R,hcetic beds are 33 feet in thickness ; at Aust 

 Cliff, 34 feet ; and at Penarth, 42 feet ; whilst at St. Audrie's 

 Slip, to the east of Watchet, and at Queen Camel, near 

 Yeovil, they have been estimated at as much as 150 feet in 

 thickness, although it is pretty certain that in both these 

 latter cases more beds, both of those overljdng and those un- 

 derlying the true Rhaetics, have been included in them than 

 is right. 



The next point to which I would direct your attention, and 

 which the Pylle Hill section illustrates very clearly, is the 

 sharp line of demarcation there is between the so-called 

 " Tea-green Marls " of the Keuper and the overlying black 

 " Paper Shales" or Avicula contorta beds of the Rhaetics. In 

 all the sections of the Rhaetic rocks in this country which I 

 know, with the possible exception of that at Watchet (and 

 this would probably turn out the same if it were more acces- 

 sible and could be examined at close quarters), the line of 

 division between these two series is as sharply defined as in 

 the present case, the lithological characters of the two series 

 are totally different, and often there are signs of slight 

 erosion of the " Tea-green Marls," which may contain in 

 small fissures and inequalities in their upper surface material 

 which has settled down into them from the overlying Paper 

 Shales; whilst a hard conglomeratic "bone-bed," or at any 

 rate a seam of pebbles, with coprolites and fish teeth, scales 

 and bones, very generally occurs at the base of the overlying 



