THE LOWEE LIAS OF KEYNSHAM. 
33 
worked belong to the Angulatus series, south of Keynsham, 
nearly the whole of the stone is derived from the lower 
Arietes series. Not only is there a marked increase in the 
total thickness of the series, but there is, at the same time, 
a great diminution in the thickness of the clay partings, so 
that the Bisulcatus zone is composed of thick limestones in 
close superposition. 
The Calcicosta series below and the Semicostatus beds 
above are very similar, in all their characters, to the beds on 
the same horizons further north. 
The hard limestone band which occurs in the lower Semicos- 
tatus beds contains Am. obliquecostatus abundantly and is 
brought into special prominence on account of its separa- 
tion, by a thick shale, from the massive limestones series 
below (the Bisulcatus beds). 
Exposure 6 . A quarry in work. 
Above the Calcicosta beds come well developed Bisulcatus 
limestones, not so thick, however, as in exposures 7 and 8. 
The Obliquecostatus limestone is strongly marked and the 
upper Semicostatus beds extremely well shown. In these 
beds. Am. turneri is a common associate of Am. geometricus. 
Exposure 7. Two small quarries close together, and a 
very large one, further to the south-west, in continuous work. 
The two small quarries only show the massive limestones 
of the Bisulcatus zone, the top block of the Calcicosta beds 
occurring at the base. Large bisulcate ammonites are 
common in the top beds, Rhynchonella triplicata and Pecten 
calvus are common throughout and an occasional specimen of 
Wald perforata can be seen in situ. 
The large quarry shows, at the base, a splendid mural 
section of the whole of the Calcicosta series, containing 
gastropods, etc., weathered out on its joint surfaces and 
identical, in all respects, with the same series further north. 
D 
