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VOL. XIV. (2) RHATIC ROCKS 163 
The overlying black, imperfectly laminated shales are 
crowded with lamellibranchs. Unfortunately, they are 
much crushed, but Avicula contorta is especially in 
evidence. A similar fossiliferous bed occurred at Wain- 
lode and Coomb Hill, and here, as at those localities, 
the succeeding deposit is greyish shale, which initiates 
the Upper Rhetic. The black shales pass so gradually 
into the greyish that lithologically an arbitrary division 
must be drawn; but the dominant factor determining the 
thickness of the former is the upward extension of Avzcula 
contorta. 
The well-known Fsthervza-bed succeeds and constitutes 
a sure datum-line upon which to correlate sections in North- 
west Gloucestershire. Four main lithic varieties may be 
noticed, namely, laminated, nodular, shelly, and that exhibit- 
ing markings analogous to those in the Cotham Marble. 
These four varieties may be traced from one into the other 
horizontally. As noticed by Mr Etheridge, in one place 
near the southern end of the cliff, nodules, with markings 
like those of Cotham Marble, rest upon a hard shelly 
limestone. A little to the north, the one may be seen 
passing horizontally into the other. 
Dr Wright had apparently observed this phenomenon, 
for he describes the bed as “a light grey, nodular lime- 
stone, in parts shelly.” The chief interest attaching to 
the stratum from a lithological standpoint, is the occurrence 
of markings similar to those exhibited in the Cotham 
Marble of the Bristol area, and often described as “ abore- 
scent” and “ dendritic.” Though the phenomena exhibited 
in the respective beds in the two districts is not similar, 
it is analogous, and doubtless has arisen from a common 
cause. The effect, however, is different, and from those 
markings in the Cotham Marble, these in the Zstherza-bed 
at Garden Cliff, may be distinguished by the absence in 
the latter of curvature in the upper laminz of the lime- 
stone, since the markings reach the surface and give rise 
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