THE AVONIAN OF THE AVON OORGE 
125 
material for studying the characters of this important zonal 
brachiopod.) 
The large exposed bedding-slope which forms the north end 
of the quarry affords an excellent opportunity of obtaining the 
dip and strike of the beds very accurately. ^ 
Resuming the traverse along the towing-path, we 
Plate XIII. reach Quarry 4 which is no longer in work. 
In this quarry the lower part of S 2 and the top of Si are 
satisfactorily exposed. 
The broad white band of Seminula-0 oIHq can be easily made 
out in the tall quarry wall. 
Large blocks of limestone crowded with Seminula ficoides, 
and others built up almost entirely of Lithostrotion Martini^ 
lie strewn over the floor of the quarry. 
>Si. 
The main interest of Quarry 4 centres, however, in the exposure 
of the Si subzone. 
The slope which forms the north end of the quarry lies 
immediately above the level of the ‘ Trilobite Bed ’ of the ‘ Great 
Quarry.’ There is, in fact, a small exposure of this bed in the 
north-eastern corner of Quarry 4 where a few trilobite tails can 
be recognized on the bedding-surface ; a frilled Athyrid, with 
the form of Athyris flanosulcata, is not uncommon but Productus 
semireticidatus, mut. Si has not been detected. 
If we now climb the main slope and examine the exposures of 
bare rock which lie in position upon it, Caninia cylindrica, mut. 
Si is seen to occur abundantly, with Lithostrotion Martini and 
Seminula ficoides. In the debris scattered over the highest part 
of the slope, at the extreme north end of the quarry, Productus d 
is abundant ; this Productus can be seen, in situ, in a bed a 
^ The observations are best made from the towing-path on the opposite 
side of the river, and the strike should be determined by walking slowly 
from south to north until the surface of this slope is just lost to view at 
the level of the observer’s eye ; the bearing of the slope at this level can 
then be most accurately read off by employing a prismatic compass. 
