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Between Poitiers and La Rochelle, the space marked A on the map separates two regions of chalk. This space is occupied by the Oolite and certain other formations older than the Chalk and Neocomian, and has been supposed by M. E. de Beaumont to have formed an island in the Cretaceous sea. Cretacee du S.-O. de la France Mem. de la Soc. Radiolites radiosa, d'Orbigny. White chalk of France. b.
The break between the Upper and Lower Cretaceous formations will be appreciated when it is stated that, although the Neocomian contains 31 species of Ammonite, and the Gault, as we have seen, 21, there are only three of those common to both divisions.
Moreover, the Baculites vagina, which is in a tolerable state of preservation, appears to Professor E. Forbes certainly to be identical with a species, so named by him, from Pondicherry in India; where it is associated with numerous decidedly cretaceous species, which approach most nearly to Lower Greensand or Neocomian forms: this fact, considering the vast distance between Chile and India, is truly surprising.
This clay is only of slight thickness in Kent and Surrey, but acquires great dimensions at Atherfield, in the Isle of Wight. The difference, indeed, in mineral character and thickness of the Upper Neocomian formation near Folkestone, and the corresponding beds in the south of the Isle of Wight, about 100 miles distant, is truly remarkable.
The lower beds of the gypseous formation resemble the corresponding and probably contemporaneous strata of the main Cordillera; whilst the upper beds in several respects resemble those of the Uspallata chain, and possibly may be contemporaneous with them; for I have endeavoured to show that the Uspallata beds were accumulated subsequently to the gypseous or Neocomian formations of the Cordillera.
Yellow limestone, which I have myself seen near Neuchatel, in Switzerland, represents the Lower Neocomian at Speeton.
In favour of this latter view, M. Marcou mentions that a fish called Asteracanthus granulosus, occurring in the Tilgate beds, is characteristic of the lowest beds of the Neocomian of the Jura, and it is well known that Corbula alata, common in the Ashburnham beds, is found also at the base of the Neocomian of the Continent.
These beds, which are without any marine equivalent in this country, appear completely to bridge over the interval between the Neocomian and the Oolites. They may, perhaps, as suggested by Mr. Judd, be of the same age as part of the Wealden series. Gervillia anceps, Desh. Trigonia caudata, Agassiz. Terebratula sella, Sowerby. Diceras Lonsdalii. Upper Neocomian, Wilts. a. The bivalve shell. b.
Professor Huxley in his late memoirs on the order of reptiles called Dinosaurians, which are largely represented in all the formations, from the Neocomian to the Trias inclusive, has shown that they present in their structure many remarkable affinities to birds.
Coal is found overlying the carboniferous limestone of the Cantabrian chain, the seams being from 5 feet to 8 feet thick. In the Satero valley, near Sotillo, is a single seam measuring from 60 feet to 100 feet thick. Coal of Neocomian age appears at Montalban.
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