northern Europe similar to that of central Asia at the present day. The Triassic deposits were then laid down, the Bunter apparently in desert lakes subject to desiccation, into which periodical streams swept sand and pebbles from the neighbouring uplands; the Keuper in a much more extensive lake or inland sea, into which the ocean at last broke and introduced the marine fauna of the Rhætic.
In Warwickshire the following subdivisions of the Triassic rocks occur:—
- Keuper Marls with Upper Keuper Sandstone.
- Lower Keuper Sandstone.
- Upper Sandstone
- Pebble Beds.
- (Lower Sandstone ?)
The Lower Bunter Sandstone which to the west of our district is so well developed in the Severn valley dies out when followed thence to the east, and has generally been thought to be absent east of the South Staffordshire coalfield; but in 1890 Mr. J. Landon called attention to the occurrence of beds of yellow sandstone below the Pebble Beds near Barr Beacon, and concluded that the Lower Bunter Sandstone is there present in force.
The Pebble Beds are well developed at Sutton Park and west of Birmingham, while a small area occurs to the east of Polesworth. The rocks consist of pebbly red coarse sandstone and impersistent beds of pebbles. These are well rounded by water action, and are chiefly of yellow, brown, and liver-coloured quartzite, white quartz, and grey crinoidal Carboniferous limestone and chert. Where two or more pebbles are in contact they have generally pressed into each other and produced a characteristic crush-mark. The source and mode of origin of these pebbles is still a matter of dispute, but the opinion of those most familiar with them is that they were derived from rocky ridges of high land which stood as islands in or formed the margins of the Triassic lake basins. Of parts of these old ridges we see the worn-down relics in the Wrekin and Caradoc districts of Shropshire, the Malvern-Abberley and Lickey ranges in Worcestershire, and the Nuneaton and Charnwood hills in Warwickshire and Leicestershire. Buckland long ago recognized that the Bunter pebbles are in many instances agreeable in substance with the quartz rock of the Lickey, and was of opinion that an extensive outcrop of this latter rock was the source of much of the Bunter material.
Exposures of the Bunter pebble beds may be seen in Sutton Park, notably in a gravel pit near Blackroot Pool. They are to be seen also on the east of the Warwickshire coalfield in a railway cutting east of Polesworth. The rock being more resistent to the weather than those above and below, generally forms a well-marked escarpment, as at Barr Beacon; the soil is generally poor and exceedingly pebbly, and is
- Proc. Birm. Phil. Soc. vii. 113. 15