﻿FRAAS ON THE JURA FORMATION. 



(il 



Am. coronatus is found in this bed, also Perna, Terebratula bipli- 

 cata, T. perovalis, and spines of Cidaris ; accompanied indeed by 

 Am. macrocephalus find Am. hecticus, which with us make their first 

 appearance in the succeeding stratum. 



Normandy also makes an exception here in the parallelism of these 

 strata. Above the light yellow limestones of the upper Lias with 

 Am. radians, Am. Thouarsensis, and Am. communis, repose the beds 

 of the Oolite inferieure, Oolite de Bayeux, or terrain bajocien, 

 with their well-known abundance of shells. In the environs of 

 Bayeux (to the W. and N.) this oolite forms a plateau, where it is 

 exposed only in ditches and quarries. The largest quarries are near 

 St. Vigor and Moutiers. Here the Oolite inferieure affords pretty 

 well all the shells that in other parts are contained in the whole of 

 the " brown Jura." But we must not imagine a great development 

 of this deposit : there are beds of about 3 or 4 feet thickness, some- 

 times coarsely, and sometimes finely oolitic, of a )^ellow colour, and 

 consisting almost of nothing else but fossils, and presenting in this 

 narrow space everything that is contained at other places in a deve- 

 lopment of as many hundred feet. Am. Murchisonce, Am. discus, 

 Am. coronatus, Am. Humphriesianus, Am. Parkinsoni, Am. hecti- 

 cus, Am. Truellei, Am. subradiatus, Am. triplicatus, Am. planula, 

 Am. macrocephalus, Am. Herveyi, Am. Brongniarti, Am. Gervillei, 

 Am. bullatus, Am. microstoma, Hamites Parkinsoni, and many 

 others, Pleurotomaria pyramidalis, PI. cadomensis, PI. ornata, PL 

 decorata, Trigonia costata, Astarte obliqua, A. depressa, Ostrea 

 pectiniformis, O. Marshii, Terebratula bullata, T. biplicata, Bel. 

 giganteus, and B. canaliculars (sulcatus) may be collected in great 

 numbers. To these must be added many rarer forms, as Natica ad- 

 ducta, Melania vittata, Corbula, Area, Auricida, Cardita, Crassina, 

 &c, all of which are in an excellent state of preservation. From 

 what is here stated, we may perceive that this oolite of Bayeux is 

 not comparable nor identified with any other bed, but is peculiar to 

 Normandy. The Swabian geologist, who knows Am. coronatus and 

 Am. Humphriesianus to be so absolutely separated from Am. Par- 

 kinsoni, and these again from Am. macrocephalus, by clays and shales 

 lying between them, sees here in one bed of 4 feet in thickness all 

 those shells together which at other places are typical of different 

 beds ; a clear proof, that in certain localities of the sea, animals of a 

 different epoch, and elsewhere separated by strata, may occur in one 

 deposit ; and that the same depositions may continue at one place, 

 which at another have been succeeded by others. By this, moreover, 

 we perceive that we have in Calvados deep sea accumulations, whilst 

 in England and Swabia littoral deposits occur. The synchronism, 

 however, of the strata specified cannot be doubted. 



Great Oolite. Bath Oolite. Bradford Clay. Forest Marble. 



Grande Oolite. Oolite de Caen. Etage bathonien (D'Orb.). CaU 

 caire de Ranville. 



Haup t-Rogens tein . 



This is the great mass of whitish yellow, oolitic rock, spreading 

 from the south of England to the west of the Black Forest, and form- 



