26 
THE LOWEE lias OP TtEYNSHAM. 
In general aspect the series bears a considerable resemblance 
to the White Lias, with its thick top block, the Sun Bed. 
Mainly composed of thin uniform beds of limestone, only 
separated by thin partings of clay, the series is immediately 
capped by a prominent bed which is very uniform in thick- 
ness throughout the district. This thick top block, being 
separated by a well-marked clay from the beds above, stands 
out as a prominent horizon in all the exposures in which it is 
seen. (How natural is the break formed by the upper sur- 
face of this block can be seen in the fact that it is used as 
the floor on which the quarryman works to remove the beds 
above, and often it forms a level top to the quarry, owing to 
its greater resistance to denudation.) This series is extremely 
rich in fossils and, where the beds have been exposed to the 
air for a considerable time, the joint surfaces are covered 
with fossils, beautifully weathered out. Small gastropods, 
belonging to several genera, range abundantly throughout the 
series, but are most prolific in the top block and in the’ 
lowest layer but one. Species of Cardinia and Astarte also 
abound, but the former are difficult to extract, since nearly 
all the specimens lie horizontally, so that the greater portion 
of their valves is firmly embedded in the stone. 
The most prolific fossil is undoubtedly the small, sharply- 
ribbed EhyncJionella ^ E. calcicosta. The top block is, in 
places, completely studded with this small brachiopod, and 
the lowest bed of the series often contains as many. Though 
this species is certainly not confined to this horizon, for it' 
ranges into the beds above and is also found much lower down 
(compare section near Bedland), yet it is so characteristic of 
this series, and so abundant in it, that the designation 
Calcicosta Beds is quite justified. The fossil cannot, however, 
be regarded as having more than a local value as a zonal 
index, for it is not recorded from Badstock, and is rare at 
Sodbury. (In Germany the same species seems to occur at a 
