INFERIOR OOLITE SERIES : BRENT KNOLL. 89 
A microscopic section of .the Doulting Stone has been given 
in the plate (p. 26) ; and' the rock has been described by 
Mr. Teall. The organic fragments appear to be mostly Grinoidal. 
I noticed that the Carboniferous Limestone at Little Elm presented 
a granular appearance somewhat similar to that of the Doulting 
Stone. A microscopic section of that older rock showed Crinoidal 
fragments, and oolite grains, in a matrix of crystalline calcite ; 
and as noted by Mr. Teall, the secondary calcite was in optical 
continuity with the organic fragments, as in the Doulting Stone. 
The same phenomena were exhibited in a microscopic section of 
Inferior Oolite from Oldford, near Frome. Evidently the In- 
ferior Oolite of this region is largely of detrital origin, being 
formed of comminuted organic remains, and the material I think 
may have been mostly derived from the Carboniferous Limestone. 
The Midford Sand, with occasional indurated bands, is found 
at the summit of Glastonbury Tor, having a thickness of about 
174 feet, and resting upon a platform of Upper Lias clay. 
The conspicuous hill of Brent Knoll stands out from the 
Alluvium of the Burnham Level between Highbridge and the 
Mendip Hills ; its height above the sea-level is 457 feet. The 
area occupied by the llomanc-British Camp, was regarded by 
Conybeare and also by William Sanders as Inferior Oolite,* 
while on the Geological Survey .Map (sheet 20) it was originally 
coloured as Marlstone or Middle Lias, the lower portions of the 
hill being regarded as Lower Lias. During the re-survey of the 
district in 1872, it fell to my lot to examine Brent Knoll, and in 
the Memoir subsequently published, a section to illustrate the 
structure of the hill was inserted.f This section represented the 
Knoll to be capped by a thin layer of the " Cephalopoda-bed " 
(below the Inferior Oolite), together with other portions of the 
Midford or Inferior Oolite Sand ; and to be based on a platform 
composed of Upper and Middle Lias. 
No natural section was to be seen at the encampment, but 
there were loose blocks of sandy and ferruginous limestone which 
contained Ammonites ; and although too imperfect for specific 
determination, the specimens were considered by Mr. Etheridge 
to belong to a type that charaterizes the so-called " Cephalopoda- 
bed," which occurs at the top of the Midford Sand in 
Gloucestershire. Since then two specimens of Rhynchonella 
cynocephala have been obtained by Mr. J. E. Clark and myself 
from loose blocks of calcareous sandstone on the summit of the 
Knoll. Specimens of Serpula also occurred, and these prevail at 
the same horizon below the Inferior Oolite in the neighbourhood 
of Beaminster and Crewkerne.J 
North of Doulting the Inferior Oolite overlaps the Lias and 
Ehastic Beds, and rests in places directly on the older rocks along 
the eastern borders of the Mendip Hills. Thus the Inferior 
Oolite rests on the Old Red Sandstone, the Carboniferous Lime- 
* Conybeare and Phillips' " Outlines of the Geology of England and Wales," 
pp. 255, 275 ; Sanders' "Map of the Bristol Coal Fields," 1862, and Proc. Bristol 
Nat. Soc., ser. 2, vol. iii. p. 44. 
t " Geology of East Somerset," &c., p. 116; Memoir on ths Lias, p. 2C3. 
J Proc. Bath Nat. Hist. Club, vol. vi. p. 125. 
