GREAT OOLITE: WILTSHIRE. 259 
We are now in a position to consider whether the Great Oolite 
is represented in any way by the Fullonian Beds of Dorsetshire. 
We have seen that where the two are developed, there no rigid 
line of division can be drawn, that where the Stonesfield Slate 
occurs the two are inseparable. Hence it is quite possible that 
south of Bradford on- Avon, the lower portion of the Great Oolite 
may be replaced to some extent by the Upper Fuller's Earth 
Clay. More than this I am not prepared to say, for it cannot be 
the case with the mass of the Great Oolite. 
The Oolite has either wedged out abruptly, or it has been 
denuded over the whole or a portion of this southern area. The 
evidence of the quarries between Bath and Bradford-on-Avon, 
shows that the Rag-beds above the Freestones become thinner 
towards the south ; but such evidence cannot be regarded as of 
much value when we remember how fickle are the majority of the 
oolites. Looking, however, at the subject from a broad point of 
view, I think we are justified in considering the case to be one of 
unconformable overlap or overstep ; in other words, that the Great 
Oolite has suffered denudation locally, and to a certain extent 
contemporaneously, so far as the Great Oolite Series is concerned. 
The Oolites as a whole are characterized by much false-bedding, 
by pauses in deposition marked by bored-surfaces, and occasionally 
by rolled masses of previously-formed Oolite. A minor amount 
of local erosion is evident, although in some instances scanty 
deposition of sediment accounts for the attenuation or local 
absence of beds. 
The Forest Marble itself is remarkably false-bedded and 
current-bedded. In its changeful series we find clays and shales, 
sands and sandstone, shelly, and oolitic limestone. The curious 
track -marks and the ripple-marks show it was deposited under 
shallow-water conditions. The numerous ochreous clay-galls 
probably originated from rolled masses of clay. While the 
structure of the oolitic beds, the grains being irregularly mingled 
with comminuted shells, and lignite, or scattered in a sandy as 
well as in a calcareous matrix, suggest the notion that they may 
have been derived. This notion occurred independently of other 
considerations, and I find it was suggested in 1879 by Dr. Sorby,* 
from a microscopical examination of specimens of Forest Marble, 
from Wiltshire and Somersetshire. He observed that the facts 
clearly show that the oolitic grains were not formed in situ, but 
were drifted along with the shell-fragments. He noticed the 
o o 
occurrence of grains of previously consolidated limestone, which 
itself was oolitic; while in other instances the rock contained 
broken grains of oolite. Still more interesting is his statement 
that, In a few cases, as at Frome, the greater part of the rock 
is composed of comminuted Corals and Polyzoa;" for it is not 
unreasonable to infer that these remains were derived from the 
Great Oolite. 
* Address to Geql. Soc. 1879, Quart. Journ. Geol. Soc., vol. xxxv. (Proc.), p. 82. 
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