356 
LOWER OOLITIC ROCKS OF ENGLAND : 
These beds have been exposed in the cutting east of the station, 
and although now a good deal obscured, a thickness of about 50 
feet may be traced as we proceed westwards. The junction with 
the Great Oolite is seen west of the station, and there we find 
laminated shaly beds, and grey and yellow marl, that yield the 
characteristic fossils of the Bradford Clay, resting On the Great 
Oolite. These basement-clays of the Forest Marble are thus 
found to be variable and impersistent in character ; grey marly 
clays occurring in lenticular masses above the false-bedded Great 
Oolite, and becoming more and more interstratified with bands of 
dark grey limestone in their course westwards towards the tunnel. 
Hence it is difficult to follow the precise horizon of the Bradford 
Clay in this direction, and the band of fossiliferous clay appears 
to die out. In this way we can understand its absence at 
Monkton Farley. 
The Great Oolite itself contains a lenticular bed of bluish- 
grey mnrly and oolitic clay 18 inches thick in places; and the 
mass of the rock exposed here, occurs in obliquely-bedded layers 
alternating with bands of harder oolite. The details of the 
junction were more readily to be noted in a quarry not far 
distant, near Brickers Barn. 
Judging by well-sections the total thickness of the Forest 
Marble in this area is from 60 to 100 feet, the strata becoming 
thinner towards Chippenham, while they may be a little thicker 
near Atford. At Corsham the subdivisions proved in a boring 
for Messrs. Randell, Saunders, & Co., were as follows : 
fBrown and blue clay and shale 
j Clay with bands of stone 
Forest Marble -< Hard blue stone - 
I Hard dead sand - 
[_Stone and clay - 
Great Oolite - Hard and soft stone 
- 12 
- 6 
- 1 
- 10 
- 16 
FT. IN. 
37 6 
9 
84 6 
A pit north-west 
following section* : 
of Brickers Barn, Corsham, showed the 
Forest Marble 
Greenish marly and racy clay - 
Very shelly and oolitic limestone (irre- 
fular and impersistent) : with Ostrea 
owerbyi, Cyprina islipensis - 
Oolitic and gritty limestone 
Shelly and oolitic limestone 
Grey marly and racy clay with thin 
layers of sandy limestone 
Hard blue oolitic and flaggy limestone 
^"Clays, and thin flaggy layers of sandy^ 1 
limestone with curious markings and 
perforations ; and a thin shelly layer 
with Apiocrinus ParTcinsoni, Oldaris, 
&c. These beds pass down into 
FT. 
1 
IN. 

* See also Lonsdale, section at Cross Keys, 9^ miles from Bath towards Ohippen- 
hara. Trans. Geol. Soc., ser. 2, vol. iii. p. 258. 
