As, however, the shells of the 2 feet 6 inches bed, described as the Cephalopoda-bed at Bradford and other places in Dorset, are identical with those at Dundry, and at both Bradford and Dundry it contains with others
|
Ammonites Parkinsoni, Sow. (A. dorsetensis, Wr.) |
Ammonites Murchisonæ, Sow. |
we conclude that the Cephalopoda-beds at Bradford and Dundry are on the same horizon, and, further, that neither the one nor the other has the slightest connexion with the Cephalopoda-bed of Gloucestershire; and if this be so, the fact that the four Ammonites just quoted have been made representatives of four distinct zones, will be a difficult problem to solve for those who implicitly believe in zones.
One of the more recent papers, "On the Correlation of the several subdivisions of the Inferior Oolite in the middle and south of England," is by Dr. Holl, who concludes that the true position of our Dorset and Somerset beds is higher in the series than is stated by the geologists just quoted, and "that they are, in fact, the southern extensions of the Upper and Lower Bagstones of Mr. Hull, the uppermost of which is not represented in the typical section at Leckhampton, having risen above the level of the country, and cropped out before reaching the brow of the hills"[1].
We agree with this view, except that we consider the Dorset Cephalopoda-bed the equivalent of the Gryphite Grit at Leckhampton, and that the roughly bedded stone above is the representative of the Trigonia Grit of Cold Comfort. The constant presence of the same typical Ammonites on the top of Leckhampton hill and in the Bradford Abbas quarries seems to prove this assertion, such as
|
Ammonites Sowerbyi, Miller. |
Ammonites concavus, Sow., M.C. |
and others.
From this, then, it follows that, while the Gloucestershire Cephalopoda-bed is at the base of the Inferior Oolite or top of the Upper Lias, the Dorset Cephalopoda-bed is near the top of the former; and yet they have not only been confounded the one with the other, but this position has been supported by the similarity, not identity, of the Cephalopoda, which, indeed, have been held to point to Lias rather than to Oolite.
Dr. Holl's view of the case seems to be, that while we have thus the Upper Ragstones, the lower members of the Inferior Oolite are deemed to be absent; for he says:—
"On the southern side of the Mendips the Inferior Oolite nowhere
- ↑ Quart. Journ. Geol. Soc. vol. xix. (1863) p. 307.
