﻿56 



GEOLOGICAL MEMOIRS. 



allied to Am. insignis, but separated from it by its form and lobes. 

 In the neighbourhood of Salins, which has become celebrated through 

 my friend H. Marcou and Dr. Germain, it is frequently found in 

 company with a legion of small silicified Ammonites. 



Besides the Ammonites there are two Belemnites, B. digitalis and 

 B. acuarius, which occur as important characteristic shells, some- 

 times together and sometimes singly, in the posidonomgce-sh&les and 

 the clays, and never appear again either above or below. The 

 Ludwig Canal especially yields an immense quantity of these two 

 Belemnites at the celebrated cutting near Rasch, and wherever the 

 laminae of the posidonGmyee-sh&les are broken, one of these Belem- 

 nites will always be found. They pass quite through France, where 

 however B. acuarius becomes more frequent ; and lastly, the large 

 and slender specimens of the English Belemnites are well known. 

 We must also particularly mention the Cyath ophyllum mactra, and 

 other small corals, which are likewise found almost everywhere in 

 this deposit, and afford a proof that it was not formed in a deep sea, 

 but in shallow water and, in part, not far from the shore. 



The following are generally characteristic of the formation : Am. 

 insignis, Am. radians with its allies, and the family of lineati, espe- 

 cially the reticulated species ; also Belemnites acuarius and B. digi- 

 talis. The entire absence of Terebratulce is also characteristic. 

 Marcou calls these beds Marnes a Trochus ou de Pinperdu. In this 

 mountain, near Salins, the clays of the upper Lias have great thick- 

 ness, are highly inclined, and afford a beautiful profile of the different 

 fossiliferous strata. Trochus duplicatus, Tr. Capitaneus, Tr. Vesun- 

 tius, Cerithium tuberculatum, Nucida Hammeri, N. claviformis, N. 

 ovalis. Area cequivalvis, and others are found here in great abun- 

 dance. These certainly are found towards the top, but in company 

 with Am. mucronatus, Am. insignis, and^fm. sternalis ; a proof that 

 we have already here the French forms, according to which the upper 

 Lias coincides with the opalinus-bed of the lower "brown Jura." 

 In the German Jura the Lias ends with this bed £, and, according 

 to all the circumstances, must be here separated from the " brown 

 Jura." With the opalinus-cl&ys there begins a distinct geological 

 series, another terrace in the gradation of the strata ; new fossils make 

 their appearance, and the relation of a. with the next stratum p. is 

 too great to allow of their separation. In France and England it is 

 otherwise ; here there exists one inseparable system of clays and 

 marls, between the posidonomyce-sh&les and the sandy limestones 

 with Am. Murchisonce. But it is quite as correct in France to 

 reckon the clays with Nucida Hammeri as belonging to the Lias, as 

 it is impossible to do so in Swabia ; because our characteristic shells, 

 Am. opalinus and Trigonia navis, are there wanting. 



B. Brown Jura. Oolite. 



The principal difference between the German "brown Jura" and 

 the French is, that here the limestones, and there the clays pre- 

 dominate. In Swabia the "brown Jura" comprehends a much 

 greater rock-mass than the "black;" but, nevertheless, on account 

 of the predominance of the clays, there is only thickness without 



