The Geological Survey of England and Wales. 
389 
The occurrence of lenticular masses of pebbles at the top of the 
Reading Beds has been noted in the Hampshire Basin. These 
possibly represent the Blackheath Beds of the London Basin. The 
Bagshot Pebble-beds have also been detected over a fairly large area 
in the Hampshire Basin. 
In West Sussex, Mr. Reid has improved the mapping of the 
Tertiary tracts. Although the strata ai’e much covered with drift, 
well-sections and other data have enabled him to carry the Eocene 
formations over a considerably larger area than is shown on the old 
map, and also to ascertain in the district the nature and importance 
of the folds and other disturbances which traverse the Secondary 
rocks of the South of England. The westward extension of these 
structural features has been traced by Mr. Whitaker through the 
Southampton district, where Bagshot Sand and London Clay have 
sometimes been thus brought up within areas hitherto believed 
to lie upon Bracklesham Beds. In Sussex these folds trend east 
and west, but in Hampshire they turn towards the north-west. 
Cretaceous . — On the older one-inch maps the Chalk was shown as 
one mass, no attempt being made to indicate its subdivisions. 
Indeed, no such subdivisions were formerly recognised, save a 
general grouping into Chalk- with- flints and Chalk-without-flints. 
Sometimes the lowest portion was separately referred to as Chalk 
Marl. In later surveys, however, advantage has been taken of the 
opportunity of tracing on the ground the subdivisions that can now 
be mapped. These are as follows : — 
Upper Chalk. 
Chalk Rock. 
Middle Chalk, with Melbourne Rock (at the base). 
Lower Chalk, with Totternhoe Stone. 
Chalk Marl. 
The Totternhoe Stone was mapped by Mr. Whitaker many 
years ago along a part of the northern side of the London Basin ; 
he also first recognised the “ Chalk Rock,” but only of late years 
have these geological horizons been represented on the maps. 
The subdivisions of the Chalk, as above described, are less 
marked in the western areas. Along the northern outcrop, 
Totternhoe Stone dies out in Berkshire, the Chalk Rock and 
Melbourne Rock continuing into Dorset and Devon. Along the 
southern outcrop, the Totternhoe Stone does not exist; and the 
other rock-beds have not been recognised west of the neighbourhood 
of Dorchester. 
The separation of the thick mass of Chalk into so many distinct 
subdivisions has both an economic and a scientific interest. By 
revealing the actual structure of the Chalk and the outcrops of its 
several members the new mapping renders essential service in 
questions of water-supply. It likewise indicates the undulations 
into which, in consequence of subterranean disturbances, the Chalk 
has been thrown. These undulations, though often too gentle to be 
safely inferred from surface exposures, are apparent when the outcrops 
of the several subdivisions of the Chalk are continuously traced.. 
