THE AVONIAN OF THE AVON GORGE 
99 
the .bed occurs at widely separated points of the Bristol 'Area 
and always at approximately the same level (for example, a 
‘ Palate Bed ’ of exactly the same type as the Avon bed occurs 
at practically the same level near Sodbury, 10 miles to the north). 
The very shallow water conditions under which this bed was 
formed are demonstrated alike by its conglomeratic characters 
and by the included mollusca. 
The ‘ Bryozoa Bed,’ which is here a massive red limestone 
about 8 feet thick, is the highest of the red beds which form so 
striking a feature in the two railway cuttings at this point. The 
rock is built up of vast numbers of small, rounded crinoid-frag- 
ments, which are cemented together by coarsely- crystalline 
calcite. It seems probable that the crinoid fragments were rounded 
by rolling in very shallow water and that the crystalline matrix 
has been produced, by solutional agency, at a time subsequent 
to the original cementation of the rock. 
The ‘ Mod^oZa-Phase.’ 
The Bryozoa Bed and the rocks below it, down to the base 
of the Carboniferous Limestone Series, can be studied equally 
well in the cutting on either of the two Avonmouth lines which 
here run close together, one at a higher level than the other. 
(The lower line is the one we have been following all the way 
from Hotwell Station ; the upper line emerges from the long 
tunnel under the Downs, at a short distance south of the Bryozoa 
Bed.) The following is a general description which applies to 
either cutting. 
The Bryozoa Bed rests upon a massive red calcareous grit, 
about 10 feet thick. 
Below this grit lie 20 feet of thin-bedded limestones, separ- 
ated by highly fossihferous shale partings, the fauna of the 
shales indicating shallow water conditions. 
Descending in the sequence, we next come upon 30 feet of 
thick shales in which a few thick beds of limestone and calcareous 
grit are intercalated 
