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
