SYNOPSIS OF FORMATIONS. 
47 
upper by a different set of forms and called 
the Devonian; resting on th^se^ and differ¬ 
ing but little in general aspect, occurs a 
succession of clays and hard strata with 
dark limestones at the base, now termed the 
Coal measures. On reaching Exeter w^e 
find the latter overlapped by masses of 
variegated sands and dark blood-red rocks, 
termed the new Red sandstone, and at the 
northern edge of this the blue Lias is super¬ 
imposed, with its well known upper associ¬ 
ates the Bath stone, Portland stone, and 
Oolites. Over these the Greensand forms a 
groupe, manifestly distinct, serving as a 
basis for the well-marked Chalk, and upon 
the latter the dark clays of London, the 
sands of Windsor forest, and the gravel of 
Blackheath rise to complete the series. 
Many minor details are omitted in this 
enumeration; a glance at a geological map 
or table, or better still, a notice of the rail¬ 
way cuttings on a journey, will serve to 
convey the outline truths of descriptive 
geology more easily than a lengthened 
enumeration of formations. 
It should he borne in mind that these 
strata are either composed of hard rock 
