LOWER CHALK —CHEMICAL COMPOSITION 
335 
The following analyses of two samples of Chalk Marl from 
Arlesey, near Hitchin, are part of a series which have been kindly 
placed at our disposal by Mr. R A. Berry. They are of special 
value because, like the analyses made by Professor J. B. Harrison , 
they are much more complete than ordinary commercial analyses 
and a special method has been devised to separate the quartz and 
the colloid silica from the clay and silicates. The carbonic acid was 
also determined in every case by direct weighing, and the amounts 
of calcium and magnesium carbonate calculated from it; the 
result being to show that a certain amount of the lime always 
remains, and this lime probably enters into the composition of 
the silicates. Of the two analyses given below, A is of the blue 
marl about 20 feet below the Totternhoe Stone (see p. 188), and 
B is of a grey marl about 6 feet below the same horizon :— 
A. 
B. 
Loss on ignition - 
- 
L30 
*24 
Calcium carbonate 
- 
50*02 
66*45 
„ phosphate 
- 
*73 
*48- 
,, sulphate 
- 
*48 
— 
Magnesium carbonate 
1*55 
*69 
Lime ----- 
3*39 
2*83 
Oxide of iron and alumina 
- 
lot 
2*08 
Oxide of manganese - 
- 
1*30 
1*27 
Clay. 
13*98 
10*06 
Quartz - 
- 
19*10 
14*28 
Colloid silica 
- 
7*30 
1*41 
Alkalis and loss in analysis 
- 
-T — 
*21 
100*22 
100*00 
Of the Chalk Marl of Cambridgeshire many analyses have been 
made in recent years for the numerous cement-making companies, 
and the two following series of analyses of successive beds at the 
same place have been kindly communicated by Mr. J. W. Knights, 
the County Analyst of Cambridgeshire: — 
Analyses of Chalk Marls from Cherry Hinton. 
1.* 
2 . 
3 . 
4. 
5. 
6. 
Insoluble siliceous matter - 
47*2 
24*6 
16*2 
21 *3 
20*1 
26*2 
Carbonate of lime 
49*0 
65*7 
70*5 
76*2 
76*5 
70*0 
Alumina and oxide of iron 
1*7 
1*6 
4*6 
1*5 
1*7 
1*7 
Magnesia and moisture - - 
2*1 
8*1 
8*7 
1 *0 
1*7 
2*1 
100*0 
100*0 
100*0 
100*0 
100*0 
100*0 
The depths from the surface at which these samples were taken were as 
below, the coprolite bed lying at a depth of 24 feet 
1 . 
2. 
3. 
4. 
5. 
6. 
5 feet. 
10 feet. 
12 feet. 
15 feet. 
20 feet. 
23 feet. 
* Some fine sand and gravel was mixed with this sample, accounting 
for the high proportion of insoluble matter. 
