A HISTORY OF BERKSHIRE 



probably once had an extension far and wide we now only find patches 

 left where beds of gravel have protected the soft strata beneath. One 

 result of this is that on the roads in the district from Newbury to 

 Windsor we find hills with a tolerably gradual ascent over the sandy 

 Bagshot Beds and a steep bit up the gravel capping at the top. 



The nomenclature of these formations is in a somewhat indefinite 

 state, but the facts are perfectly clear and simple. 



There are three formations as already mentioned : 



1. The Bagshot Beds or Lower Bagshot Beds. 



2. The Bracklesham Beds or Middle Bagshot Beds. 



3. The Barton Beds or Upper Bagshot Beds. 



The Bagshot or Lower Bagshot Beds are about 100 feet in thick- 

 ness, and consist of yellow sand with a little clay in places and here 

 and there a few flint pebbles. 



There is no satisfactory record of fossil shells from these beds in 

 Berkshire, but evidence from Surrey is in favour of the view that the 

 upper part at least was deposited in salt water. The sands show 

 much sign of currents, and probably the truth is that they were like the 

 underlying strata deposited in or near the mouth of the estuary of a 

 great river which was subsiding, and that at some times the salt water 

 advanced further up it than at others. 



This division of the Bagshot series frequently yields a very soft 

 and pure water; owing however to the porous character of the beds 

 the water is liable to surface pollution. 



The Bracklesham or Middle Bagshot Beds rest on the Lower Bag- 

 shot ; they are composed of light-coloured sandy clays, green and yellow 

 sands with occasionally beds of stiff dark-coloured clay and usually some 

 layers of flint pebbles. 



The beds of green-coloured sand are found more or less well 

 developed and often contain pyrites and fossil wood. Beds of lignite 

 occasionally occur. 



The greatest thickness is about 50 feet. Fossils are scarce, but 

 here and there casts of shells occur in some abundance and occasionally 

 the shell is preserved. Corbula, Cardium and a large Cardita together 

 with a small oyster are fairly common. The valves are always or almost 

 always united, and probably the shell fish lived where we now find them. 

 They are all salt water forms ; many casts of these shells were collected 

 from a cutting just within the county on the railway between Ascot and 

 Bagshot, and specimens will be found in the Museum of Practical 

 Geology in Jermyn Street. 



The water found in the Bracklesham Beds is usually of an unsatis- 

 factory character. The clays are worked for brickmaking near Ascot, 

 etc. 



The Barton or Upper Bagshot is again a sandy series, indeed it 

 consists practically of yellow sand. The greatest thickness is about 

 200 feet. The only fossils found in Berkshire are very indistinct casts 

 of shells ; better specimens have however been discovered in Surrey, 



18 



