336 
THE CRETACEOUS ROCKS OF BRITAIN. 
Analyses of Chalk Marls from Barrington. 
1. 
2. 
3. 
4. 
5. 
6. 
Insoluble siliceous matter - 
14-10 
18-10 
19-40 
21-60 
24*60 
33-00 
Carbonate of lime 
83 • 20 
78-90 
77-24 
74-50 
71-50 
62-20 
Alumina and oxide of iron 
1-70 
1 -60 
2-10 
2-10 
2 • 30 
2*80 
Magnesia and moisture - 
1/00 
1-50 
1-26 
1 -80 
1-60 
2-00 
100-00 
100*00 lOO'OO 
1 
100-00 
100-00 
100*00 
No. 1 was taken at 4 feefrfrom the surface. 
No. 2 ,, 6 ,, ,, 
No. .3 „ 7 
No. 4 „ 16 „ ,, 
No. 5 „ from the bottom of the cement material. 
No. 6 „ from the layer overlying the coprolites. 
The Marl at Cherry Hinton seems to have been worked under a 
bed of gravel and sand, and the infiltration of sandy material from 
this seems to have extended as deep as 10 feet from the surface. 
At 12 feet, however, we seem to have a pure mail containing 16 
per cent, of siliceous matter, and the proportion of this increases 
downward till it amounts to 26 per cent. 
The other series from Barrington shows a regular increase of sili¬ 
ceous matter from 14 to 33 per cent., with a corresponding decrease 
of calcareous material from 83 to 62 per cent., the lowest sample 
being evidently taken from the glauconitic marl which overlies the 
“ coprolite bed.” 
Mr. Knights, however, informs me that the relative proportions 
of calcareous and siliceous material are not always so regularly 
distributed as in this case, even at Barrington itself, and that so far 
as the carbonate of lime is concerned the proportion varies in an 
uncertain and irregular manner. This is illustrated by a series of 
samples taken from the face of a trench at Barrington which Mr. 
Knights tested for carbonate of lime only with the following 
results: — 
First Series. Second Series. 
Depth from 
surface. 
. 
Proportion of 
CaCOj- 
Depth from 
surface. 
Proportions of 
CaC0 3 - 
F eet. 
F eet. 
3 
67*5 
1 
79*0 
5 
6 1 * 5 
3 
74*5 
7 
74*0 
5 
73*0 
9 
84 
7 
85 * 5 
11 
70 
9 
88*0 
13 
72 
11 
68*0 
15 
76 
13* 
67*5 
17 
62 
15 
- 
74 '0 
The following are three more detailed analyses of Chalk Marls 
from Cambridgeshire, the first two having been made and communi¬ 
cated bv Mr. J. W. Knights, and the third by Mr. H. Bassett 
(communicated by Mr. G. Ik Gildea). The sample No. 1 was from 
