104 
THE AVONIAN OF THE AVON GORGE 
The ‘ Bryozoa Bed ’ which caps the massive band of red rocks 
is best examined in a thin slice under the microscope. Bryozoa 
belonging to the genus Rhabdomeson are always to be seen, but 
they are relatively scarce in comparison with the great number 
of small rounded sections of crinoid fragments which constitute 
the main portion of the slide. These crinoid sections exhibit a 
finely reticulate structure suggestive of the transverse sections 
of dendroid Bryozoa, and it is to their great abundance that the 
rock owes its misnomer. [There are several beds in the upper 
part of the Cleistopora-Zone to which the title of Bryozoa Bed 
might be much more aptly applied.] 
The index fossil, Modiola lata, is to be found throughout the 
Modm/a-Phase, but it is most abundant in certain of the shales 
included in Division (c). The horizon at which it is most prolific 
is a shale bed in the Lower Cutting, 30 feet below the top of the 
‘ Bryozoa Bed,’ where it is associated with enormous numbers 
of small Ostracods. 
= Subzone of Productus bassus. 
Diagnosis : 
Productus bassus, Chonetes cf. Buchiana and Eumetria afi. 
carbonaria are abundant at certain levels. 
Fauna: 
Productus bassus. 
Chonetes cf. Buchiana. 
Chonetes cf. crassistria. 
Chonetes cf. hardrensis. 
Local detail: — 
In the Lower Cutting, Ki extends from above the Palate Bed 
up to the low wall which terminates the exposure, and it will be 
sufficient to examine only the lowest and highest beds in this 
series since the intermediate beds (some 20 feet of shales and 
thin limestones) are not richly fossiliferous. 
The basal limestones, 2 or 3 feet in thickness, are crowded 
with fossils, and from them, all the forms cited above should 
be obtained, with the exception of the three species of Chonetes 
Orthothetes cf. crenistria. 
Le'ptaena cf. analoga. 
Eumetria aff. carbonaria. 
Camarotmchia mitcheldeanensis. 
