| NAMES OF SYSTEMS | | SUBDIVISIONS | | CHARACTERS OF ROCKS |
| --- | --- | |
| TERTIARY | ||
| | Metal Age Deposits | | | |
| Recent | | Neolithic Deposits | | Superficial Deposits |
| Pleistocene | | Palaeolithic Deposits | | |
| | Glacial Deposits | | | |
| --- | --- | |
| | Cromer Series | | | |
| | Weybourne Crag | | | |
| Pliocene | | Chillesford and Norwich Crags | | Sands chiefly |
| | Crags | | | |
| | Red and Walton Crags | | | |
| | Coralline Crag | | | |
| --- | --- | |
| Miocene | | Absent from Britain | | |
| --- | --- | |
| | Fluviomarine Beds of Hampshire | | | |
| | Bagshot Beds | | | |
| Eocene | | London Clay | | Clays and Sands chiefly |
| | Oldhaven Beds, Woolwich and Reading Groups | | | |
| | Thanet Sands | | | |
| --- | --- | |
| SECONDARY | ||
| | Chalk | | | |
| | Upper Greensand and Gault | | Chalk at top, | |
| Cretaceous | | Lower Greensand | | Sandstones, Mud and |
| | Weald Clay | | Clays below | |
| | Hastings Sands | | | |
| --- | --- | |
| | Purbeck Beds | | | |
| | Portland Beds | | | |
| | Kimmeridge Clay | | | |
| | Corallian Beds | | | |
| Jurassic | | Oxford Clay and Kellaways Rock | | Shales, Sandstones and |
| | Cornbrash | | Oolitic Limestones | |
| | Forest Marble | | | |
| | Great Oolite with Stonesfield Slate | | | |
| | Inferior Oolite | | | |
| | Lias--Upper, Middle and Lower | | | |
| --- | --- | |
| | Rhaetic | | | |
| | Keuper Marls | | | |
| Triassic | | Keuper Sandstone | | Red Sandstone and |
| | Upper Bunter Sandstone | | Marls, Gypsum and Salt | |
| | Bunter Pebble Beds | | | |
| | Lower Bunter Sandstone | | | |
| --- | --- | |
| PRIMARY | ||
| | Magnesian Limestone and Sandstone | | Red Sandstones and | |
| Permian | | Marl Slate | | Magnesian Limestone |
| | Lower Permian Sandstone | | | |
| --- | --- | |
| | Coal Measures | | Sandstones Shales and | |
| | Millstone Grit | | Coals at top, | |
| Carboniferous | | Mountain Limestone | | Sandstones in middle, |
| | Basal Carboniferous Rocks | | Limestone and Shales below | |
| --- | --- | |
| | Upper | Devonian and | | Red Sandstones, | |
| Devonian | | Mid | Old Red | | Shales, Slates and, |
| | Lower | Sandstone | | Limestones, | |
| --- | --- | |
| | Ludlow Beds | | Sandstones, Shales and | |
| Silurian | | Wenlock Beds | | ThinLimestones, |
| | Llandovery Beds | | | |
| --- | --- | |
| | Caradoc Beds | | Shales, Slates, | |
| Ordovician | | Llandello Beds | | Sandstones and |
| | Arenig Beds | | Thin Limestones | |
| --- | --- | |
| | Tremadoc Slates | | | |
| Cambrian | | Lingula Flags | | Slates and |
| | Menevian Beds | | Sandstones | |
| | Harlech Grits and Llanberis Slates | | | |
| --- | --- | |
| | | | Sandstones, | |
| Pre-Cambrian | | No definite classfication yet made | | Slates and |
| | | | Volcanic Rocks | |
| --- | --- |
If we could flatten out all the beds of England, and arrange them one over the other and bore a shaft through them, we should see them on the sides of the shaft, the newest appearing at the top and the oldest at the bottom, as shown in the table. Such a shaft would have a depth of between 10,000 and 20,000 feet. The strata beds are divided into three great groups called Primary or Palaeozoic, Secondary or Mesozoic, and Tertiary or Cainozoic, and the lowest Primary rocks are the oldest rocks of Britain, which form as it were the foundation stones on which the other rocks rest. These may be spoken of as the Pre-Cambrian rocks. The three great groups are divided into minor divisions known as systems. The names of these systems are arranged in order in the table and on the right hand side the general characters of the rocks of each system are stated.
With these preliminary remarks we may now proceed to a brief account of the geology of the county.
Sectional Diagram
This cross section shows what would be seen in a deep cutting nearly E. and W. across England and Wales. It shows also how, in consequence of the folding of the strata and the cutting off of the uplifted parts, old rocks which should be thousands of feet down are found in borings in East Anglia only 1000 feet or so below the surface.
In Cornwall there is a succession of nodes of granite rising to the surface, a continuation westward of the mass of Dartmoor. It has surged to the surface in four large masses continued westward by the Scilly Isles. These granitic masses have upheaved the superincumbent beds of stratified rocks, partly melting them. These distinct nodes are: the Bodmin moors, the St Austell elevation, the Carn Menelez, and the Land's End district. Smaller masses of granite occur in the double heights of Godolphin and Tregonning, St Michael's Mount, Carn Brea and Carn Marth, and Castel-an-Dinas.
The Cheesewring