GIBB — OYSTER CONGLOMERATE BED AT BROMLEY. 329 
many of the oysters were strangers to the spot on which they are now 
found, from the very great preponderance of single valves over the 
perfect shell, as well as finding many of the latter in over-turned 
positions. The following are the fossils which I obtained from this 
excavation ; there are other species of Ostrea and Cerithium besides 
those named : — 
Ostrea bellovicina. Serpula vermicularis. 
,, edulina. Vermilia triquetra. 
Cyrena cuneiformis. Perforations of Clionidaa. 
Cerithium variabile. Minute scales of fish. 
Pectunculus Plumsteadiensis. Indistinct traces of plants. 
Modiola Mitchelli. 
At the railway cutting, a quarter of a mile to the south-west of 
Bromley, a section of the same deposits is to be seen running through two 
high hills, consisting of gravel, layers of sand, and shell breccia, but 
the last consists of small shells, with comparatively few oysters, and 
not so many rolled flints at this spot. Throughout the whole of 
Bromley, on digging for wells, this conglomerate has invariably to be 
reached before water can be obtained; one well shown to me gave a section 
of two feet of loam, two feet of gravel, twelve feet light grey and brown 
sands, and seven feet of oyster-conglomerate ; a plentiful supply of water 
had been reached at this depth. This occurs when the dry and hard 
rock, especially at the surface of the conglomerate, has been cut 
through. 
The Lower London Tertiaries are divided into three sub-groups by 
Mr. Prestwich, the upper one, which is called the " Basement-bed of 
the London clay," is a marine deposit, resembling the beds beneath it 
in mineral character, but in organic life more nearly related to the 
London Clay above it. The middle sub-group, or the " Woolwich and 
Beading Series," is a very variable group of freshwater and sestuarine 
origin. The lower sub-group, or the Thanet sand, is a marine bed of 
much less extent than the other two. These three groups are ably 
described in the third lecture of Mr. Prestwich' s, " The Ground Beneath 
TJs."* 
* Visitors to Bromley can avail themselves of the services of Mr. Porter, the 
enterprising landlord of the " Rising Sun," who will undertake to pilot them to 
the railway-cutting, the rock-pit, and the underground chalk-quarry. 
