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CHAP. VI.
MESOZOIC STRATA.
219
are not coextensive, at least their calcareous portions: the upper or Portland limestone is the most limited and interrupted; the lower or Bath rocks are the most extensive and connected, but at the same time, perhaps, the most variable. These and other results will appear in the following comparative table, suited to the north and south of England.
| Peculiar to the North. | Common to both. | Peculiar to the South. |
| Wealden clay. Hastings sand. Purbeck beds. | ||
| Kimmeridge clay. | Portland oolite. Sands. | |
| Upper calcareous grit. Coralline oolite. Lower calcareous grit. Oxford clay. Kelloways rock. |
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| Carbonaceous gritstones and shales. | Cornbrash and clays. | Hinton sandstones and sands. |
| Carbonaceous gritstone, shale, and coal. | Great oolite. Inferior oolite and sand. |
Forest marble and clay. Fullers' earth rocks. |
| Upper lias shale. Marlstone beds. Middle lias shale. Lias limestone. Lower lias shale. |
If, comparing Britain with Europe, we view the oolitic system in gross, we shall find as the most general result, three considerable groups of rocks, viz.:—
Upper group, consisting of arenaceous (wealden) formation;
Middle group, consisting of the calcareous (oolitic) formations;
Lower group, consisting of the argillaceous (lias) formation;
and may consequently view the whole as a succession of argillaceous sediments widely disseminated in the sea,
