60 On the Phosphoric Strata of the Chalk Formation. 
fields, but of those of his neiaihbours, for some distance on either 
hand, and that thus a band of country of many miles in breadth, 
and extending with the chalk through this island in more than one 
direction, may experience the advantage of a cheap supply of one 
of the most valuable of mineral manures. Whether or no these 
advantages may be confined to the localities of the chalk forma- 
tion, it is difficult at present to say ; such information as it is in 
the power of the authors to afford him the reader will find in the 
following account of the phosphoric strata, which it is the inten- 
tion of the paper to introduce to his notice. 
The series of strata termed by geologists the Cretaceous 
system does not consist exclusively of chalk, as the name implies, 
but comprises a large proportion of both sand and clay in the 
definition. It will be necessary, however, for the elucidation of 
the special object of the present paper, to refer occasionally to 
members of the whole group, although the principal deposits 
largely impregnated with phosphoric acid are confined to specific 
zones in certain subdivisions of the strata. Many of these divi- 
sions abound in fossil shells, corals, &c., which are exclusively 
of marine origin ; these, with the occasional presence of drifted 
wood, generally perforated by marine animals, prove the formation 
to have been deposited at the bottom of an ancient sea. 
The crelaceuus group has been divided into the chalk and green-sand 
formations ; and these again subdivided — the former into 
1. Soft white chalk with flints; 
2. Hard white chalk with few or no flints ; 
3. Chalk marl ; 
and the green-sand formation into 
1. Upper greeu-sand and firestoue rock ; 
2. Gault, or blue marl ; 
3. Lower greeu-sand — made up of iron-sand and occasional limestone. 
An inspection of a geological map of England will show the ranges 
and extent of the chalk group. 
One range commences at Flamborough Head in Yorkshire, and runs 
in a S.W. direction to Burv St. Edmund's, and continues without much 
interruption through Wiltshire and Dorsetshire to Sidmouth in Devon- 
shire. A second, constituting the North and South Downs, commenc- 
ing at Dover in Kent, runs through Surrey to Alton in Hampshire 
(where it unites with the former range, extending across the whole 
county into Wiltshire), and then turns back through Sussex to Beachy 
Head. The tlriid comprises the southern half of the Isle of Wight. 
The first two divisions of the chalk formation, viz. the soft 
white chalk with flints and the hard white chalk without them, 
are so extensively developed in many parts of the kingdom, and 
their general characteristics are so well known, that it will be 
unnecessary to occupy the pages of the Journal by any minute 
description. Wherever these sections of the chalk are not thickly 
