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rarely in the Sherborne district. South of the Mendips it is 
not found in any great variety until in the Fuller’s Earth rock, 
and then not of such size as in the Cotteswolds. One of the 
Cotteswold varieties of this species is the parent of the Tereb. 
intermedia of the Cornbrash. 
Rhynchonella hampenensis (S. Buckm.) also migrated from 
the Cotteswolds and is found in the Castle Cary district; it is 
not found in the Sherborne district or in South Dorset. 
Acanthothyris spinosa is found of very fine proportions in 
the Cotteswolds, and in the Castle Cary district; but it is 
smaller further south. Rhynchonella angulata (Sow.) is a species 
peculiar to the Cotteswolds (Parkinsoni-zone, Upper Trigonia 
grit.) | 
This migration of species took place during the Parkinsont- 
zone, a time when we suppose the barriers, which prevented 
the Brachiopoda of previous zones from migrating, had been 
broken down by subsidence. 
Towards the close of the Parkinsoni-zone some changes 
occurred which induced most of the mollusca to leave these ° 
areas; and we find that an almost unfossiliferous white lime- 
stone— generally a freestone—is common to Dundry, the South 
Cotteswolds, the Bath-Mendip district, and part of the Dorset- 
Somerset area. 
We now take our leave of Dundry, for all traces of the 
succeeding formation—the Fuller’s Earth—have been removed 
from that hill by denudation; but it is instructive to briefly 
glance at the course of events in the other areas. 
A deposit known as Fuller’s Earth Rock stretches from 
near Bath into the Dorset-Somerset area, shewing that though 
the old Mendip barrier had been overcome, there was still some 
cause preventing the occurrence of this deposit in the Cottes- 
wolds. With the advent of the Great Oolite period, it would 
seem as if the Mendips were able to re-assert themselves ; for 
this formation is not found south of that range. Scattered 
patches of Bradford Clay probably indicate a tendency of the 
Oolitic sea-floor to ridge up and form itself into more or less 
isolated districts. (It is curious to notice that a deposit of this 
