238 
THE GEOLOGIST. 
compiled for the Holraesclale Natural History Club, at EeijSfate, by Mr. 
Brewer. The work is in small octavo, and contains nearly 370 pages, and 
two large excellent folded maps — one of the geology, the other botanical 
provinces ; and it will be useful to add, that the geological map can be 
purchased separately in sheet, case, or on rollers. In accordance with 
Mr. Salmon's plan, the county has been divided into nine districts or 
divisions, for the purpose of more readily ascertaining the particular loca- 
lities of the plants. Tlie geological map has been prepared and coloured 
from one drawn by Mr. Prestwich, and we need not say will consequently 
be acceptable to all who are interested in the geology of the county. 
The three principal groups of geological strata are the Wealden, the 
Cretaceous, and the London Clay ; Reading and Woolwich beds, Thanet 
sands, and other Tertiary beds surmounting the Chalk. Here and there, 
especially along the river-valleys, are accumulations of gravel and drift 
deposits. The whole of the north-eastern division of the county belongs 
to the London Clay formation, and is comparatively low; and consequently 
the various elevations on the north side, such as Denmark, Herne, and 
Richmond hills, although of no great elevation, still command extensive 
prospects. It also forms the hills running southward along the Kentish 
border by New Cross, Forest Hill, Sydenham, and Norwood. It is 
estimated that in some situations the London Clay is nearly a thousand 
feet thick, but that that portion which extends into Surrey does not exceed 
500 or 600 feet. The principal feature of the norlhern district is again 
the London Clay, covered in places by the Bagshot sand, as in the vicinity 
of Esher. The whole of the north-western division consists of London 
Clay, for the most part covered with the Bagshot sand, and presenting a 
poor, hungry, unimprovable soil, as at Bagshot heath itself, which lies within 
this region. Large masses of the siliceous sandstone known as "grey 
wethers " are found there. The entire eastern division is occupied by the 
Cretaceous rocks, with the exception of a small portion of the Heading 
and Woolwich beds, and the Thanet sands, which occur to the east of 
Croydon. The Chalk occupies a considerable area, and forms a portion of 
the North Downs. The Upper G-reensand, or freestone, forms the foot of 
the escarpment of the Downs, and extends from Godstone by Merstham 
and Reigate through the county into Hampshire. The central division is 
principally occupied by the Chalk, but its north-west angle shows London 
Clay, which at Ockham Heath and Send is covered with Bagshot sand ; 
and a narrow slip of the Woolwich and Reading beds runs along the 
northern margin of the Chalk. The western division is principally occu- 
pied by London Clay, but a narrow ridge of chalk, known as the " Hog's 
back," runs almost the whole length of the southern boundary, and at the 
foot of which the Gault and Upper Greensand crop out. The south-eastern 
division is, with the exception of a narrow strip of Lower Greensand on 
the north, occupied by the Weald Clay — the Hastings sand appearing at the 
south-eastern corner. The southern division is equally divided between 
the Greensand and Weald Clay. The principal stratum in the south- 
western division is the Lower Greensand. 
The following is a brief analysis of the distribution of the plants : — 
The total number of species occurring is 117 ; the number confined to the 
valley alluvium, 7 ; to the superficial gravels, 19 ; to the Bagshot sands, 9 ; 
to the London Clay, 14 ; to the Reading and AVoolwich beds, 2 ; to the 
Chalk, 55 ; to the Upper Greensand and Gault, 5 ; and to the Lower Green- 
sand, 28. 
