o46 MR. E. WILSON ON A SECTION OF 



information relating to it so meagre — probably because the railway- 

 cutting when examined was already in great measure defaced — 

 that it is practically valueless. A re-description of the Pylle-Hill 

 section therefore appears desirable whilst it is in a fresh state. In 

 a very short time, indeed, the new cutting, which, like the old one, 

 is sloped at so high an angle as to be almost inaccessible, will 

 become obscured by rainwash and vegetation, and thus be no longer 

 available for detailed examination. 



The first thing that strikes one in the Pylle-Hill section is the 

 very limited development of the Rhaetic Beds, the whole series, 

 according to my estimate, measuring only seventeen feet, or not 

 more than half the thickness which they usually attain in the West 

 of England *. At Wcstbury-on-Severn, for instance, the Rha3tic 

 Beds are 33 feet thick, at Aust Cliff 34 feet, and at Penarth 42 

 feet. 



There can scarcely be any doubt as to which is the true base of 

 the Rhajtic at Pylle Hill, but it is possible there may be some 

 difference of opinion regarding its upper limit. The precise point 

 where the line should be drawn between the Lias and the E-haDtic 

 in the West of England is still a matter of some uncertainty, our 

 chief Rhaetic authorities, Moore, Wright, Etheridge, Tawney, 

 Dawkins, and H. B. Woodward, having taken very different views 

 on this question. At the base of the Lower Lias we generally find 

 a variable series of light grey to cream-coloured limestones and 

 shales, which are commonly called " White Lias." This quarry- 

 man's term for these beds is, however, an unfortunate one, for since 

 it was first adopted by William Smith, in the year 1815, it has been 

 applied by different authors to very different things — some at any 

 rate of the rocks which it covers being certainly Ehaetic, whilst 

 others are as certainly Lias. In the Pylle-Hill section, I take the 

 three or four feet of light-coloured rubbly limestones and finely 

 laminated shales o,p, ^, r, to represent the so-called "White Lias." 

 The fossils of these beds are bivalve molluscs mostly in the condition 

 of indeterminable casts, but we can make out with certainty 

 Modiola minima^ Monotis decussata, a Lima (apparently Lima 

 <)igantea\ and a Pleuromya. The presence of these shells, and the 

 absence of characteristic Ehaetic forms, induces me to class these 

 beds with the Lias rather than with the Ehaetic. I take the bed 

 n of my section, which is evidently the equivalent of the '^ Gotham 

 Marble " or " Landscape-stone," as the highest distinctive Ehaetic 

 rock in this section. Probably some authors would include in the 

 " White Lias " not only the beds o to r, but also the underlying 

 light grey shales and limestones weathering white, from i to n. 

 AVhatever we choose to call them, these latter rocks are certainly 

 Ehaetic, the bed i, for instance, containing such characteristic EhcTtic 

 fossils as Cardium rhceticum, Pecten valoniensis, Schizodtis Ewaldi, 



* Fourteen years ago the Ehaetic "Beds were penetrated in an excavation for 

 the foundations of the Bristol Waterworks Pumping Station, Oakfield Road, 

 Olifton, on the north side of the city, and were there shown by the late Mr. E. 

 B. Tawney, F.Gr.S., to be only sixteen feet in thickness. Proc. Bristol JVat. Soc. 

 n. s. vol. ii. (1878) p. 179. 



