THE CRETACEOUS ROCKS OF BRITAIN. 
If the magnesia is present as a carbonate in all these samples, the carbo¬ 
nates of lime and magnesia in each are probably as follows 
A. 
B. 
C. 
D. 
E. 
Carbonate of lime 
Carbonate of magnesia 
92*29 
1 *61 
94*25 
1 *57 
79*84 
1*26 
91 *61 
*52 
93*04 
1*47 
The sample of the Inoceramus-bed from near Gayton (C), is remark¬ 
able for containing so much phosphoric anhydride, equivalent to 5*5 per 
cent, of calcium phosphate. , The amount of calcium carbonate would 
seem to be only 79*84 per cent., but there are some difficulties in re¬ 
constructing the mineral composition of the rock from this analysis. 
In the case of C Dr. Johnstone also made a further analysis of 
the insoluble portion with the following results : 
Insoluble part of C. 
Silica - - - -. 5*547 
Alumina -.* 900 
Ferric oxide - *560 
Calcium oxide -.*107 
Magnesium oxide ------- trace 
Phosphoric acid - - - - - - - trace 
Organic matter . *440 
7 * 554 
This appears to indicate that the greater part of the insoluble residue is 
fine quartz sand, with some clay and a little organic matter. 
The following are three analyses of samples from the Lower 
Chalk of Speeton, made for Mr. W. Hill by Mr. J. W. Knights, 
of Cambridge.* The first (A) was a bluisli-grey chalk taken 
about 6 feet above the top of the Bed Chalk (Selbornian); B was 
taken near the top of Bed 3 where it is pink ( i.e ., about 36 feet above 
the Selbornian). C is a whitish chalk from Bed 7, about 12 feet 
below the Belemnite marl. 
A. 
B. 
C. 
Insoluble siliceous matter - 
3 
- 
12*40 
5*40 
6*00 
Carbonate of lime - 
--- 
- 
82*40 
92*80 
89*80 
Carbonate of magnesia 
- 
- 
1 *80 
*75 
1 *66 
Oxide of iron and alumina - 
- 
- 
1 *40 
*80 
1*00 
U ndetermined matter - - - 
- 
- 
2*00 
*25 
1 *54 
100*00 
100*00 
100*00 
It will be noticed that all these beds contain rather a large amount of 
siliceous matter, which is probably chiefly in the form ol clay; this is 
especially large in the lowest bed, which in this respect presents a great 
contrast to the whitish limestone at the base of the Chalk along the 
western outcrop in the Wolds of Yorkshire and Lincolnshire. 
It is somewhat remarkable that the pink chalk (B) should contain a rather 
larger amount of calcareous material (93*55 per cent.) than the whitish 
chalk from a much higher horizon (C), which has only 91*46 per cent. 
* 
See Quart. Journ, Geol, Soc., Yol. xliv. p. 358 (T888). 
