LOWER CHALK—MICROGRAPHIC STRHCTl/RE. 
297 
Summary of Chemical Results. 
In this zone the proportion of material insoluble in the acid solu¬ 
tion is on the whole considerably less than in the Chloritic marl, but 
the results of the analysis of the specimens appear at first sight 
irregular, not only when the zone is considered laterally from west 
to east, but also when considered in different localities in vertical 
section, the percentage of insoluble matter ranging from 3*03 
per cent, at Hunstanton to 46 • 19 per cent, at Arlesey, in the 
latter case in the upper part of the zone. 
The specimens from the West of England contain by far the 
largest proportion of coarse ingredients. In the two samples of 
the quartziferous limestones of Devonshire analysed by Dr. Hume, 
the coarse particles, i.e. } sand grains, glauconite, silicified shell-frag¬ 
ments and foraminifera amount to 5’33 per cent, and 18*74 per 
cent, respectively. Though there is so large a proportion of coarse 
material, the clayey residue is comparatively small, the analysis 
showing that only 1*78 per cent, and 2*82 per cent, of fine matter 
is present in the two samples. Two specimens obtained from 
Mupe Bay at 10 feet and 20 feet above the base of the zone also 
contain a large amount of coarse material, the percentage being 
11*82 per cent, and 3 * 27 per cent, respectively, the analysis show¬ 
ing a progressive decrease of coarse matter upwards, but this decrease 
is only in the coarse material, for there is a slight increase (5 per 
cent.) in the proportion of the clay. 
Taking the results of the analysis of a series of specimens which 
are given below, we see that the coarse part of the residue diminishes 
10 ft. above the 
Base of the Zone. 
Mupe 
Bay. 
Cerne. 
Isle of 
Wight. 
Folke¬ 
stone. 
Arlesey, 
Beds. 
Carring¬ 
ton, 
Cambs. 
Hun¬ 
stanton, 
Norfolk. 
Speeton, 
Yorks. 
Per cent, of coarse 
residue. 
11-82 
4-62 
1-44 
1-35 
•31 
•28 
•14 
•31 
Per cent, of fine 
residue. 
15-45 
10-11 
23-31 
35-95 
24-07 
21-58 
4-73 
15-83 
Total per cent, of 
resin ue 
27-27 
1478 
26-75 
37-30 
24-38 
21-86 
4-87 
15-84 
from west to east, but the percentage of fine material, the clay of the 
deposit, while showing a tendency to drop between Mupe Bay and 
Gerne, rises at the Isle of Wight and again at Folkestone, then 
decreases northward at Arlesey and again at Barrington, and 
becomes very small at Hunstanton. From the evidence of thin 
microscopic sections this condition of things continues to north¬ 
east Yorkshire, where at S pee ton there is again an increase of mud. 
A second series may be taken from the foregoing table of samples 
between 20 feet and 45 feet above the base of this zone. Some re¬ 
markable differences occur here which must be considered in detail. 
