148 Analysis of Scientific Books. 
The chalk formation from its extent and contents forms one 
of the most remarkable and interesting features of English 
geology. Where in contact with the superincumbent clay it 
generally exhibits symptoms of having been exposed and worn 
previous to its having received that covering, as if an interval 
had existed between its completion and the deposition of the 
formations that repose upon it. The upper strata of chalk are 
remarkable for their layers of nodular flints, which are generally 
arranged nearly in a horizontal position. Sometimes tabular 
masses, and even veins of flint, are observed, the latter travers- 
ing the strata at various angles. Nodules of pyrites, and of 
crystallized carbonate of lime are also found in these beds, and 
a very interesting series of organic remains of genera and species 
nearly all extinct. The lower strata of chalk are marked by 
the deficiency of flint and organic remains, and are commonly 
more or less argillaceous, exhaling an earthy smell when 
breathed upon, and degenerating into what is usually called 
chalk marl, a compound of chalk, clay and sand. Where chalk 
is of uniform texture, it is generally deficient in springs; but 
where it happens to be traversed by beds or veins of substances 
of softer or sabulous texture, there the water often percolates and 
yields an abundant supply. The agricultural qualities, and the 
aspect of chalk are too well known to require particular notice. 
A loose siliceous sand, occasionally aggregated by a calcareous 
cement, and containing particles of mica and green earth, forms 
the stratum upon which the chalk rests, and which is of consi- 
‘derable thickness in the southern counties, but more obscure 
in the midland and northern counties. The fuller’s earth, and 
sulphate of barytes of Nutfield in Surrey, together with crystals 
of quartz, and carbonate of lime, and nodules of chalcedony 
and chert, are found in this deposit; it is also very abundant 
in organic remains. It is, however, difficult to draw any cor- 
rect line of demarcation between this green sand with its accom- 
panying clays, and the great tron sand formation, which we see 
in such perfection in the cliffs at Hastings. This iron sand, 
however, is comparatively scanty in organic remains, so that 
the green sand and iron sand bear in this respect some analogy 
to the upper and lower chalk. 
Weare sorry that our limits prevent us following our authors 
into the valuable details, which they have selected with much judg- 
ment and diligence, connected with the localities of the chalk forma- 
tion and its associates, but they do not admit of an intelligible 
abridgment: indeed, we think the work is occasionally a little 
obscured by an attempt at brevity ; at least, by an endeavour to 
bring under one point of view a great assemblage of local pecu- 
liarities and minutiz, many of which might have been more 
conyeniently thrown into notes at the foot of the page, or 
