376

PHYSICAL GEOGRAPHY OF THE OOLITE. [Ch. XX.

Middle / d ■ Coral ra £'

1 e. Oxford clay, and Kelloway rock.

I f. Cornbrash and Forest marble.

g. Great Oolite and Stonesfield slate.

h. Fuller’s earth.

i. Inferior Oolite.

The Lias then succeeds to the Inferior Oolite.

The Upper Oolitic system of the above table has usually theKimmeridge clay for its base ; the Middle oolitic system, the Oxford clay. The Lower system reposes on the Lias, an argillo-calcareousformation, which some include in the Lower Oolite, but which willbe treated of separately in the next chapter. Many of these sub-divisions are distinguished by peculiar organic remains; and,though varying in thickness, may be traced in certain directionsfor great distances, especially if we compare the part of Englandto which the above-mentioned type refers with the north-east ofFrance and the Jura Mountains adjoining. In that country, distantabove 400 geographical miles, the analogy to the accepted English type, notwithstanding the thinness or occasional absence of theclays, is more perfect than in Yorkshire or Normandy .

Physical geography .—The alternation, on a grand scale, of dis-tinct formations of clay and limestone has caused the oolitic andliassic series to give rise to some marked features in the physicaloutline of parts of England and France . Wide valleys can usuallybe traced throughout the long bands of country where the argilla-ceous strata crop out; and between these valleys the limestones areobserved, composing ranges of hills or more elevated grounds.These ranges terminate abruptly on the side on which the severalclays rise up from beneath the calcareous strata.

The annexed cut will give the reader an idea of the configurationof the surface now alluded to, such as may be seen in passing fromLondon to Cheltenham , or in other parallel lines, from east to west,in the southern part of England. It has been necessary, however,

Fig. 367.

Lower Middle Upper London

Oolite. Oolite. Oolite. Chalk, clay.

Lias. Oxford Clay. Kira. clay. Gault.

in this drawing, greatly to exaggerate the inclination of the beds,and the height of the several formations, as compared to theirhorizontal extent. It will be remarked, that the lines of cliff, orescarpment, face towards the west in the great calcareous eminencesformed by the Chalk and the Upper, Middle, and Lower Oolites ;and at the base of which we have respectively the Gault, Kim-meridge clay, Oxford clay, and Lias. This last forms, generally, abroad vale at the foot of the escarpment of inferior oolite, but whereit acquires considerable thickness, and contains solid beds of marl-stone, it occupies the lower part of the escarpment.