] PROCEEDINGS OF THE GECLOGICAL SOCIETY. 
synchronism of the Bognor beds of Hampshire to the lower part 
only of the London clay. 
In his second communication, Mr. Prestwich describes the sands 
resting upon the London clay, and commonly known as the: Bagshot 
sands, from their exposure in the vicinity of that town. He divides 
these sands into lower, middle and upper Bagshot sands, respectively 
of the thickness of 100 to 150 feet, 40 to 60 feet, and 250 to 300 
feet ; the middle division contaming the greater amount of clays, 
with one or two beds of green sands. The Bagshot sands are con- 
sidered by our colleague equivalent, though comparatively poor in 
organic remains, to the rich fossiliferous deposits of Bracklesham in 
the Hampshire district, and as synchronous with the central vertical 
strata in White-Cliff Bay, and with the great central mass of varie- 
gated and light-coloured sands of Alum Bay, including probably the 
Barton clays, and as being at all events older than the freshwater 
or fluvio-marine series. Mr. Prestwich regards the Bagshot sands 
as forming an uninterrupted sequence of deposits to the London clay, 
and that they may be represented in the Paris tertiary district by the 
lower part of the Calcaire grossier and Glauconie grossiére. 
Taking a general view of the tertiary accumulations in the western 
London and Hampshire districts, (for he considers that there are other 
beds developed beneath the London clay in. the eastern London di- 
strict,) Mr. Prestwich divides the deposits into three chief groups: the 
first, or lowest, argillaceous, consisting of the mottled clays and London 
clay, containing a few subordinate beds of sand, chiefly confined te 
the former, its fauna presenting forms of which a considerable pro- 
portion is restricted to it. The central group embraces the Bagshot 
and Bracklesham sands; and the third or upper group contains 
accumulations of freshwater or fluvio-marine origi. All the groups 
are developed in Hampshire, while in the West London district the 
two lowest only are discovered. 
These inferences of Mr. Prestwich not being deductions from hasty 
examinations, but the result of careful investigations and of long-con- 
tinued labour, we may regard the views he has taken as placing us 
in a position respecting the Parisian equivalents of our tertiary de- 
posits in Southern England, and of these with each other, far in ad- 
vance of that which we previously occupied. So much of these 
tertiary accumulations has been removed by denudation, which has 
not only cut away a large amount of these rocks, but of those also 
which supported them, that great difficulties may always attend our 
endeavours to ascertain the shores washed by the sea durimg the 
accumulation of these tertiary beds, or the range of the deeper or 
shallower portions of it, at successive times, during the lapse of the 
same geological period. However this may be, the labours of Mr. 
Prestwich, who in the papers before us has combined lithological 
descriptions so carefully with paleontological comparisons, are in 
the right direction. It is from such investigations that we may ex- 
pect a still more extended knowledge of our tertiary deposits, up to 
the changes now in progress inclusive, not restricting ourselves to 
supposed marked groups, the names for which, however convenient 
