THE LOWEK LIAS OF KEYNSHAM. 
37 
combeia are the predominant fossils. A single, thick band of 
compact limestone, containing Am. plmiorbis^ forms the base 
of the Psilonotus zone, as it does at Redland, Radstock and 
Stoke Gifford. The ammonite is in places very abundant. 
Immediately above the Planorhis bed come several thick 
beds of limestone, crowded with Am. johnsfoni and large 
Limas ; both Lima gigantea and Lima liermanni reach their 
maximum in these beds, but L. gigantea is by far the most 
abundant.. Pholadomya glabra links the beds with the 
Ostrea beds below, whilst 0. irregularis and smooth Pectens 
of the calvus type occur here, but reach their maximum in a 
higher zone. 
Immediately on top of the Psilonotus limestones is a thin 
clay, succeeded by a limestone, both of which contain 
Echinid fragments in profusion, as well as abundant specimens 
of large Limas. This horizon corresponds to the Echinid 
Bed shown in the north Keynsham sections, which usually 
consists of a thick clay, but is liable to pass laterally into 
limestone, as we have already noted in exposure 3. 
Above the Echinid Beds comes a thickness of six feet 
mainly composed of clay, but containing a band of thin 
argillaceous limestones a little above the middle of the series , 
as well as a thin band of rubbly limestone nearer its base. 
The lower rubbly band contains few fossils {Wald perforata 
was noted), but in the middle band fossils are fairly abundant 
and, amongst these, Am. angulatus is not uncommon. From 
the presence of this ammonite and the absence of Rli. 
calcicosta and Gryphea arcuata, the whole of this series may 
be classified as Ostrea irregularis beds (lower Angulatus 
zone). Here we have another instance of the lateral passage 
of limestones ^ and clays into each other, for these beds, 
which further west are mainly composed of limestone beds 
with subsidiary clays, are here represented by thick clays 
with a few subsidiary limestone bands. 
