1848. | WESTON ON THE GEOLOGY OF RIDGWAY. 251 
21-23. Plaited oysters; two species, but I cannot pretend to name 
from such morsels without good geological and local evidence.”’ 
Am. Arduensis and Am. Marie are quite new in the fossil concho- 
logy of England, but they have been found in the Jurassic formations 
of France: No. 8 in the equivalent of the Oxford Oolite, and No. 9 
in that of the Oxford clay. 
On carefully reviewing the above list of fossils we shall, I think, 
feel satisfied that the deposit which contained such remains must be 
the Oxford clay. 
I will merely add, that accompanying these Ridgway fossils are 
two Modiolas,—one procured from the Oxford clay of Wiltshire (be- 
tween Laycock and Melksham), and the other I myself found im the 
upper part of the cornbrash and just below the Oxford clay at Wey- 
mouth. Mr. Sowerby has compared these with Nos. 16 and 17 of 
the preceding list, and considers the Wiltshire fossil as undoubtedly 
the same species as No. 16, and the other (from Weymouth) as 
probably the same with No. 17*. 
Proceeding upwards in the geological series, I shall now refer to 
the greensand. This formation, although not exposed in the cutting, 
ought I think to be considered as existing and as making another 
addition to the already comprehensive stratification. It is visible at 
Bincombe within a mile on the east of Ridgway, and the chalk-marl 
met with by the two shafts shows us how near the level of the cutting 
is to the base of the chalk of the Ridgway range. 
At Bincombe the greensand is seen to dip at about 20° to the north, 
with the supermcumbent chalk reposing conformably upon it. I 
think therefore we may infer that the chalk of Ridgway is also ele- 
vated in a similar manner ; indeed, reasoning @ priori, we might be 
led to conclude that this chalk would be influenced by the general 
upheaving of the district. 
Connecting the section, from the base of Ridgway Hill to its 
summit, with the strata to be found between Upway and Weymouth, 
we shall have within the distance of four miles the followmg remark- 
able extent of geological sequence—a sequence perhaps not to be 
paralleled in any other locality of equal limits. 
1. Forest marble. 7. Portland stone. 
2. Cornbrash. 8. Purbeck beds. 
3. Oxford clay. 9. Hastings sands. 
4. Oxford oolite. 10. Chalk. 
5. Kimmeridge clay. 11. Tertiary. 
6. Portland sand. 
Having spoken of the beds which the railway cutting has just 
brought to light, I shall now add some remarks on the Portland and 
* Since the transmission of the last two specimens of Modiolas, I have examined 
some parts of the Oxford clay of Wilts, in the vicinity of the cornbrash, and I 
have found that the Oxford clay towards its junction with that formation rather 
abounds in the Modiola. The idea therefore which I originally entertainéd, when 
in Dorsetshire, that there was at least an intermixture of the lower part of the 
Oxford clay in the Ridgway cutting, seems to be confirmed, and I cannot but add 
that the peculiar position of this argillaceous deposit, and the hypothetical causes 
which have been assumed as producing its protrusion, appear to me to derive in- 
creased probability from this fact. 
