14 STRATA EXPOSED IN CONSTRUCTING FILTON-AVONMOUTH RAILWAY. 
The lower part of the vertical section (frOm the White Lias to 
the Keuper) was constructed from data supplied by the Charlton 
cuttings, mde page 7. 
(C) The Hallen Cutting. 
The only other cutting of importance on this railway is at Hallen, 
about one mile West of the Charlton cutting. Here the Keuper 
marls are well displayed ; they consist of thick beds of red marl with 
bands of a bluish grey colour at more or less regular intervals. The 
beds exhibit the same undulatory character that has been observed 
in the Charlton cutting. 
An extraordinary deposit of Gypsum occurs near the western end 
of this cutting. It appears in nodular masses many feet in thickness. 
Some thousands of tons of this rock, for which a ready market was 
found, have already been extracted. At present the cutting is about 
20 feet deep ; it will ultimately reach twice this depth in places, 
but, judging by the excavations made for piers of bridges &c., no 
lower formation will be disclosed. 
III. CORRELATION OF THE RH^TIC AT CHARLTON 
WITH PYLLE HILL. 
The correlation of a series of deposits bed by bed, even in con- 
tiguous areas, must always be attended with rloubt and diJliculty. 
But since, in most of the recent local work on the Rhsetic, some 
attempt has been made to bring the sections into line with the one 
at Pylle Hill described by the late E. Wilson, it is perhaps desirable 
to give the following table of suggested equivalents at Charlton — 
Pylle Hill, Charlton. Pylle Hill, Charlton. 
Upper Rh^tic. Lower RHiETic. 
n = 
1 
h = 
13- 
-15 
m = 
2—9 
g z= 
16 
1 = 
10 
d, e, f = 
17 
k = 
11 
c = 
18 
i = 
12 
a', b = 
19 
a = 
20- 
-21 
IV. VARIATION IN THICKNESS OF THE RH^TIC. 
Reference to the diagram on page 15 will make clear the variation 
in thickness of the Rhsetic deposits, so far as they are known, on a 
line drawn from Pylle Hill, just South of Bristol, to Sedbury, in 
Monmouthshire. A section of the Lower Rhsetic at Garden Cliff, 
14 miles N.N.E. of Sed'nury, is given for comparison. The diagram also 
indicates the position of the more constant and easily recognised beds. 
The Cotham marble is recognised at all the sections excepting Garden 
Cliff. The upper Fecteri bed occurs in all the sections ; apparently 
it is the most constant hard bed in the Lower Rhsetic of this district. 
The lower Pecten bed is not recognised as such at Pylle Hill, Red- 
land, or Sedbury; but, at Pylle Hill, a “thin pyritic sandstone,” and 
at Redland a “ ferruginous band ” separates the crumbly shale above 
from the harder unfossiliferous shale below. 
