Lower chalk—mtcrcxlraphic structere. 
273 
Summary of Chemical Results. 
It is believed tliat the treatment by a weak solution of hydro¬ 
chloric acid (20 per cent.) removes little but the carbonates of lime 
and magnesia contained in the specimens examined; therefore the 
first column of the foregoing table, which gives the percentage 
soluble in acid, represents fairly well the amount of lime plus the 
small quantity of magnesia which chemical analysis shows to occur 
in many chalks. 
It will be seen by reference to the table that the smallest pro¬ 
portion of fine mud is found in examples from South Wilts and 
Dorset, where it does not exceed 16 per cent. Eastward it in¬ 
creases to nearly 20 per cent, in the Isle of Wight, and north¬ 
eastward to 41 per cent, in Hertford, 28 per cent, in Norfolk. The 
Chloritic Marl of Folkestone, however, contains only about 8 per 
cent, of fine inorganic matter. 
Further examination shows considerable differences in the coarse 
residues. Thus in the Folkestone specimen no less than 65*95 per 
cent, consisted of coarse particles readily separated by levigation 
(the coarse residue), while those from Maiden Bradley contained 
56*79 per cent, and 43*29 per cent, respectively of coarse ingre¬ 
dients, and the lower part of the bed at Mupe Bay yielded 42*11 
per cent, of such constituents. At Cerne there was only 7*86 
per cent, and in the upper part of the mass at Mupe Bay only 
3*02 of coarse material. 
There is, however, a great difference in the constitution of 
these coarse residues, for while glauconitic grains formed 94 per 
cent, of that from Folkestone, the two from Maiden Bradley 
contained only 19’63 per cent, and 10*68 per cent, respectively. 
The Maiden Bradley, examples, however, far exceed that of Folke¬ 
stone in the amount of sand-grains they contain, the detrital 
minerals being estimated to form 72*43 per cent, and 81*30 per 
cent., but in the Folkestone sample the amount of the detrital 
minerals is only 2 per cent, of the coarse residue. These 
details are still more striking* when the proportions are calculated 
in relation to the mass of the rock ; it will be found then that the 
sand-grains form 37 per cent, of the sample from the top of the rock 
at Maiden Bradley 24 \ per cent, in the lower sample from 
Mupe Bay, 11J per cent, in the Isle of Wight, 7 per cent, at 
Shouldham, 2J per cent, at Cerne, and only 1\ per cent, at Folke¬ 
stone. It is remarkable that the amount should be so small at 
Cerne, for Mr. Teall has identified in this rock all the minerals found 
at Maiden Bradley. 
The proportions of glauconite calculated in the same way are 
61 per cent, at Folkestone, 14J per cent, at Mupe Bay, 12 per 
cent, at Ventnor (base of Bed 5), 9 per cent, at Maiden Bradley, 
and 3 per cent, at Shouldham. 
