PRE-CARBONIFEROUS FLOOR OF THE MIDLANDS. 
165 
As the coal supply diminishes from the exhaustion of 
the present proved areas, such experimental borings will 
doubtless be undertaken. 
Relations of the Post-Silurian strata to the Midland Axis .— 
There is no evidence of the extension of the Old Bed Sandstone 
to the east of the Severn. Whether it was formed in a lake, 
or in a delta, it is probable that it was prefcty well confined 
to the region where it is now exposed. The Carboniferous 
rocks thin from north to south in the most marked manner 
as they approach the Charnwood-Longmynd line. There is 
a thin impure representative of the mountain limestone on 
the north-west flank of Charnwood, but even this is absent 
(together with the millstone grit) in Warwickshire and 
Staffordshire. It is true that the Northampton borings 
yielded fossils of this age, but they were from sandstones 
and marls, the shallow water representatives of the grand 
3,000 feet thick deep-sea limestone of Derbyshire. 
The manner in which the South Staffordshire coal- 
measures rise up and terminate against a sub-terrestrial ridge 
of Silurian rocks on the south of Halesowen has already 
been described. 
Of the succeeding Permian strata, we find that in Notts, 
the Magnesian Limestone (Lower Permian) decreases from 
above 100 feet at Shireoaks to 30 feet at Bulwell; showing 
that as we pass southwards we are approaching its ancient 
limit or shore-line, the region round Charnwood Forest. 
Westward, in South Staffordshire and Shropshire, the 
Permians are thicker, but they show every sign of the 
presence of land immediately to the south during the time 
of their formation. South of the line of the ancient axis 
we get no indications of Permian strata; they are wanting in 
all the borings made in this direction, and they nowhere 
occur at the surface. 
The Tnassic Formation, above 3,000 feet thick in 
Cheshire, and possibly of equal thickness in Yorkshire and 
Durham, thins away steadily (the lower beds disappearing 
first) to the south. The Bunter Pebble Beds barely reach to 
Leicestershire ; their thickness decreasing from above 300 
feet in Cannock Chase to a mere band of 10 feet in the 
railway-cutting at Gresley in north-west Leicestershire, and 
the borings further south show only a small thickness of the 
“ red rocks,” and that of a littoral nature, between North¬ 
ampton and London. Between the Malvern and the Mendip 
Hills the Bunter Beds (Lower Trias) are absent, and a thin 
layer of the Keuper, evidently a shore deposit, rests on 
Devonian and Carboniferous rocks. 
