298 
CRETACEOUS ROCKS OF BRITAIN. ' 
20 to 45 ft. above the 
Base of the Zone. 
Mupe 
Bay 20ft. 
above 
base. 
Isle of 
Wight 
? 20ft. to 
25ft above 
Base. 
*Folke- 
stone soft 
20 above 
Base. 
Folke¬ 
stone 
35ft above 
Base. 
Arlesey 
45ft above 
Base. 
Hunstan¬ 
ton 6ft. 
below 
Tot. stone. 
Speeton 
15ft below 
the Grey 
Bed. 
Per cent, of coarse 
residue. 
3-27 
•767 
•47 
•17 
•20 
•01 
•013 
Per cent of fine residue 
16-02 
39-03 
27-41 
21-96 
45-99 
3-02 
5-038 
Total per cent, of 
residue. 
19-29 
39-80 
27-88 
22-13 
46-19 
3-03 
5-051 
* Not included in the regular series. 
The first, from Mupe Bay, as already noted, shows a decrease in 
the amount of coarse residue in that locality; but in the next, 
a specimen from the Isle of Wight, taken from Dr. Hume’s 
Micro-Mineralogical Researches, which, judging from the descrip¬ 
tion given, was obtained from 20 feet to 25 feet above the base of 
this zone, shows a decided increase of the fine material not only 
when compared with Mupe Bay, but also when compared with a 
specimen lower in the zone from another locality in the island 
(Compton Bay). 
Dr. Hume also records the analysis of a specimen of chalk from 
Culver Cliff, Isle of Wight, which he refers to the zone of 
Holaster subglobosus. The specimen yielded a residue of 44*85 
per cent, on treatment with the acid solution. From Dr. Hume’s 
description of the horizon and the results of our own analyses 
of chalk of the zone of Holaster subglobosus at the Isle of Wight, we 
felt sure that this specimen came from the upper part of the beds 
which are now taken as the zone of A.varians, and we have included 
it in this division. Our surmise as to the horizon of this specimen 
proved to be correct, for, having had an opportunity of consult¬ 
ing Dr. Hume, he agrees that the chalk from which he took the 
specimen is part of that which we include in the lower zone. 
There is therefore a still greater increase in the amount of terrigenous 
material in the upper part of this zone in the Isle of Wight. 
But such increase is by no means exceptional. At Arlesey the 
amount of clay 45 feet above the base is neady double the amount 
in the basal specimen—viz., 46 * 19 per cent., compared with 24 * 38 
per cent. Professor Judd records a residue of 50 per cent, from 
Chalk Marl of the Richmond boring. * 
It is important to notice that this increase is not in the coarse par¬ 
ticles, but chiefly in fine mud ; so fine indeed is it at Arlesey that it 
is impossible to separate the minute mineral grains from the rest 
of the deposit, though in thin sections they are easily seen to be very 
numerous when the rock is viewed under the microscope. Though 
this high percentage of clay falls again at Arlesey towards the summit 
of the zone, it is even then large compared with any sample just 
above the base. 
* Quart. Journ. Geol. Soc., Vol. xlii. p. 435. 
