254 LOWER OOLITIC ROCKS OF ENGLAND: 
has remarked " that no satisfactory divisisn of the Great Oolite 
could be made by means of the coral-fauna."* 
Oppel took the Bradford Clay with the Great Oolite, and 
grouped them as the zone of " Terebratula digona " : while he 
placed the Forest Marble and Cornbrash in the zone of " Terebratula 
lagenalis"\ We cannot, however, separate Bradford Clay from 
Forest Marble. 
Ammonites arbustigerus has been taken on the continent to 
indicate the horizon of the Great Oolite. It belongs to a group 
that includes A. subcontracts, A. bullatus, and A. viator. The 
A. subbakerice, of d'Orbigny, which occurs in the Bathonian of 
the Bus Boulonnais, may also (if it be not identical with one of 
the above-named forms) be considered to belong to the group. 
A. arbustigerus has been recorded from the Fuller's Earth of 
Somerset and from the Great Oolite of Minchinhamptou. It 
occurs also in Normandy. We may therefore class the beds 
from the Fuller's Earth or Fullonian to the Forest Marble as the 
zone of Ammonites arbustigerus^ 
LOCAL DETAILS. 
Bradford-on-Avon to Bath. 
Relations of Great Oolite to Fuller's Earth and Forest Marble. 
One of the problems in Jurassic geology is the disappearance 
of the Great Oolite south of Bath.J It forms the dominant 
features around the city, and stretches northwards and westwards 
to Minchinhampton, Cirencester, and Stonesfield. It is exten- 
sively mined at Box and at Bradford-on-Avon; but it tapers 
away between Wellow and Norton St. Philip, at a distance of 
about 6 miles south of Bath. 
So few geologists have expressed any views on the subject that 
what has been said may be readily quoted. 
The Rev. W. D. Conybeare remarked in 1822, that " The whole 
mass of this oolitic system in Dorsetshire (excepting the inferior 
oolite and its sand) presents the fissile character of the forest 
marble ; but it seems more probable that the great oolite- here 
passes into this structure (as it undoubtedly does occasionally in 
other places), than that the forest marble, generally a subordinate 
bed only, should here swell to such a disproportionate thickness, 
and the great oolite itself be wanting." 
Lonsdale seven years later, in his excellent account of the 
Oolitic District of Bath, after referring very briefly to the dying 
out of the Great Oolite, remarks " It might, however, be con- 
ceived, that the termination is only a lithological change, and 
* Quart. Journ. Geol. Soc., vol. xxxijc. p. 174. 
f Juraformation, p. 443. 
J H. B. W., Geol. Mag., 1888, p. 467; and Rep. Brit. Asoc. for 1888. p. 651. 
See also Proc. Geol. A.SSOC., vol. xiii., p. 133, and Fig. 1. 
Outlines of the Geol. Eng. and Wales, p. 205. 
