98 
THE AVONIAN OF THE AVON GORGE 
overgrown and consequently the rocks can only be examined 
in bare patches. It is not until we have passed the level cross- 
ing and reached the end of the low wall, which is there built 
up against the bottom of the slope, that a good section of the 
rocks is again exposed for examination. From the base of the 
Black Rock massif to this point, all the beds may be assigned 
to the upper subzone of the Cleisto'pora-ZoiiQ. They consist of 
thick shales, interbedded with thin-bedded, argillaceous lime- 
stones. The general type of sedimentation indicates muddy 
water of moderate depth, under standard conditions. 
Lower subzone (K J [including the ‘ Modiola-Vhd^se.^] 
Plate II now examine the section in the short cutting, 
north of the level crossing to which we have already 
referred, we are at once struck by the massive red beds which 
are termed the ‘ Bryozoa Beds.’ 
Resting on these beds, and extending southward as far as the 
end of the low wall mentioned above, are a series of thin-bedded 
limestones with shale partings. This portion of the sequence is 
the only part of Kj which' was deposited under standard condi- 
tions ; the whole of the lower portion of Ki consists of sediments 
accumulated under special conditions in ext;remely shallow water. 
The separation of Ki into an upper and a lower division, charac- 
terized respectively by standard and special conditions, is much 
sharper in the Avon sequence than in any other part of the 
South-Western Province. The ‘ Bryozoa Beds ’ mark the 
junction of the two divisions and the ‘ Palate Bed,’ which lies 
some 3 or 4 feet above the top of the ‘ Bryozoa Bed,’ may be 
taken as the base of the normal development of Kj. 
The ‘ Palate Bed ’ is a thin, very hard conglomeratic bed, 
full of coprolites and containing the teeth and spines of fish 
in considerable abundance. Like all ‘ bone beds,’ the hori- 
zontal distribution of this bed is extremely patchy (at one 
point the bed is well developed, whereas at another, only 
a short distance away, it is practically absent) ; nevertheless, 
