﻿GEOLOGICAL MEMOIRS. 



such size and abundance as near Neuhausen, Jungingen, Margareth- 

 hausen, and Lochen. On the other hand the variety of Am. Jason 

 is here entirely wanting, which Ammonite is found most abundantly 

 near Gammelshausen and Heiningen. Am. Lamberti is everywhere 

 rather rare, as well as Am. athleta and Am. Bakerice. In Switzer- 

 land and Mont Jura the distribution of shells is quite different. 

 Monte terribile, Belfort, Besancon, Salins, and Andelot are rich locali- 

 ties for the ornati-clsijs. The chief fossils here are Am. Lamberti, 

 Am. annularis, and Am. hecticus, whilst our Am. ornatus and Am. 

 Jason have disappeared, and are only found (silicified) lower down in 

 the Callovien. Belem. hastatus is also general as a characteristic 

 form. 



These clays, exhibiting the above-mentioned paleeontological dif- 

 ferences, yet always remaining similar in appearance, extend through 

 France (in Burgundy, where limestone predominates, they are here 

 and there wanting) to the sea. Between Trouville and Dives these 

 clays {Argiles de Dives) re-occur in full force in the lofty cliffs, called 

 Vaches noires, formed of argillaceous and calcareous masses, and ex- 

 posed to the continual erosive action of the violent breakers of that 

 coast. Here sections of the strata from the Great Oolite upwards to 

 the Greensand are exposed to view. Those of the " Brown Jura" 

 consist of clay-beds, in which Gryphcea dilatata is found at almost 

 every step. The brown oolitic Kellovian limestone-bed (erroneously 

 named by the Norman geologists after the English " Calcareous 

 grit"), with calcified Am. Lamberti, Am. caprinus, and Am. perar- 

 matits, divides the black clays into two distinct portions, which have 

 only Grypluea dilatata in common. In the upper part we find sili- 

 cified Ammonites (Oxford-clay), below the Callovien only Bivalves 

 and Gasteropods (Combrash) ; the sea washes the shells out of the 

 three beds, and throws them on the shore mixed together ; in this 

 case their respective beds are not recognised, and hence all which is 

 black clay has been regarded as Oxford-clay. In the true Oxford- 

 clay re-appear only Am. ornatus and Am. Jason. Here occur Am. 

 Lamberti, very thick and large, Am. sublcevis, Am. athleta, Am. 

 perarmatus, Am. caprinus, and Am. macrocephalus. Everything is 

 silicified and preserved with rare beauty ; the size of the shells is 

 especially to be admired ; they surpass the Swabian specimens three 

 or even six times. Am. athleta, Am. perarmatus, and Am. Lamberti 

 attain 1 — 1 J foot in diameter, and are changed into pure quartz of 

 metallic lustre. Pecten Jibrosus and Trigonia clavellata, the latter 

 forming whole beds above the clays, occur here, but are not found in 

 Swabia. 



The same conditions obtain on the other side of the Channel : 

 Am. athleta, Am. Jason, Am. sublcevis, and Am. Comptoni (convo- 

 lutus) are characteristic in the environs of Oxford ; at some places 

 the chambers of the Ammonites are filled with white calc-spar. 

 Christian Malford, near Chippenham, has yielded large supplies of the 

 shells peculiar to this formation ; they are mostly ornati, crushed, 

 nacreous, and with the mouth well-preserved. Am. Jason, with a 

 lip an inch long, is termed Am. Elizabethce ; the lip of Am. convo- 

 lutus is quite as long. Together with these are also found, besides 



