16 STRATA EXPOSED IN CONSTRUCTING FILTON-AVONMOUTH RAILWAY. 
V. POSITION OF THE BONE BED. 
There are, in many Rh^tic sections, deposits at different levels 
which are more or less bone beds in character. At Charlton, for 
example, the basal part of the Upper Rhsetic — West of the tunnel — 
and the lower Pecten bed, contain in places all the constituents of 
a bone bed as defined by Mr. W. H. Wickes.i Such deposits may be 
found both above and below the bone bed now under discussion. This 
bed is distinguished by having its vertebrate contents more evenly 
distributed, in greater abundance, and by its position in the general 
sequence. For, the evidence now available tends to the conclusion 
that such beds were in process of formation, at approximately the 
same date, over a large area. 
It is true this bed is found in different localities at varying distances 
above the base of the Rhsetic series, but the explanation of this fact, 
suggested by Mr. L Richardson, appears to meet the case satisfactorily. 
He remarks that, “ There is evidence to suggest that there were earth- 
pressures at work at the close of the Keuper Epoch, which caused 
the deposits to be thrown into slight synclinal and anticlinal flexures. 
In the depressed areas the earlier deposits of the Rhsetic were laid 
down, and successive overlap on to the marls seems to have taken 
place,” 2 
In this view it would of course be futile to attempt any correlation 
of the bone beds at different localities, by comparing their position 
in relation to the amount of Rhsetic deposit below. The only method 
of correlation applicable to this case is to note their relation to 
succeeding deposits of more constant character, and therefore of less 
doubtful identity. 
Some assistance to this end may be obtained by the application of 
a table compiled by Prof. Reynolds and Dr. Vaughan, giving a 
general sequence of Rhsetic deposits as exhibited by all the local 
sections. 
General sequence of the Rh^tic,^ 
Gotham marble. 
Upper 
Rh^tic 
Lower 
Rhsetic 
f V. Shales, Ostracods and Estheria ... 1 Description 
\lV. Shales maximum of Estheria .../ abridged. 
HII, Dark shales (usually with one or more beds of dark 
limestone), the maximum of Pecten valoniensis. 
II. Black shale, with occasional thin sandy bands, contain- 
ing the maximum of Avicula contorta, and probably 
also of Schizodus Ewaldi and Myophoria postera 
I. Non fissile black shale with few fossils. Beds poor in 
mollusca^ but frequently teeming with vertebrate 
remains. 
This Table has been applied in Diagrams I. and II. 
^Bristol Naturalists Society’s Proceedings. New series, Vol. X (1904), p. 219. 
“2 Quart. Journ. GeoL Soc., Vol. lx. (1904), p. 356. 
® Quart. Journ. Geol. Soc., Vol. lx. (1904), p. 199. 
