398 



THE GEOLOGIST. 



beds, leaving those who desire fuller information to obtain it from the 

 book itself, which offers an admirable model for the production of similar 

 works in our own country. Such works on local geology are too few 

 with us, and are generally too poor, both in ability and information, 

 to merit regard ; it is most commendable therefore to promote the desire 

 for this class of productions on every occasion that presents itself, and a 

 better model for a simple geological sketch could not be taken than the one 

 before us. 



The arrondissement of Montbeliard is situated at the extreme frontier 

 of France, near the Vosges, in a depression which separates those moun- 

 tains from the northern Jura. It consists almost entirely of the Jurassic 

 formation ; but outcrops of the Triassic and masses of other rocks are how- 

 ever met with. 



The Trias is divided into Gres higarrS (variegated sandstone), Calcaire 

 comhylien (Muschelkalk), and Marnes irisees (Keuper). 



The Jurassic formation offers eight subdivisions— the Lower, Middle, 

 and Upper Lias, the Inferior and Great Oolites, and the Oxford, Coralline, 

 and Ximmeridge series. The base of the Lower Lias is a yellowish-white 

 quartzose sandstone, four to five metres thick, full of casts of Carditiia 

 and other bivalves, and corresponding to the Gres d'Hettanges. Over this 

 follows the dark grey Calcaire a Gryphees arquees, attaining the thickness 

 of ten to twelve metres. The Middle Lias presents, at its base, grey or 

 blue marls and dark-coloured, marly, fragile limestones, slightly schistose ; 

 these are the 3£ames a Grypliaa cymhium. The second group is formed of 

 blue limestone, disposed in nodules in regular beds, alternating with 

 narrow beds of marl — Calcaire a Belemnites. The third group, the Marnes 

 a Ajnmonites margaritaUis, consist of dark grey shaly marls. The Marnes 

 a Plicatules, the fourth and last group of the Middle Lias, alternate with 

 marly limestones. They are always micaceous and sometimes sandy. The 

 thickness of the whole division is about thirty metres. The Upper Lias is 

 divided into three groups, the Schistes hitumineux, the Ifarnes a Trochus, 

 and the Gres supraliasique. The first consists of very friable, argillaceous 

 schists, highly impregnated with bitumen ; the second are firm grey or 

 hitish marls ; and the last is formed of nodules and fine layers of very 

 friable sandstone, very micaceous, alternating with sandy clays charged Avith 

 mica, and known as the Marnes micacees. The thickness of the division 

 is from twenty to thirty metres. The principal fossils in the upper beds — ■ 

 Ammonites insignis, Scliubl. ; A. primordalis, Schl. ; A. hifrons, Brug. ; 

 Trochus diqjlicatus, Sow. ; Leda rostralis, Lara. sp. ; Nucula Sammerii, 

 Defr. ; Astarte VoUzii, Hoen. The Inferior Oolite commences with red- 

 dish or yellow limestones, enclosing regularly stratified beds oi' hydroxide 

 of iron, the Oolitlie ferrugineuse. Above this is the Calcaires a Entroques 

 (entrochital limestone). Then, again, the Calcaires a 'Polypiers, enclosing 

 siliceous nodules. The thickness of this group, over fort}^ metres in the 

 Jurassic chains, is considerably reduced at the northern extremity of the 

 arrondissement. The Oolitic iron is an excellent mineral, and supplies a great 

 many of the factories of Franche-Comte. There are important mines in it 

 worked by the Compagnie des Forges from Audincourt to Dampjoux, near 

 the mouth of the Barbeche. The Entrochal limestone furnishes a building 

 stone of very excellent quality, which is almost exclusively employed at 

 Besanyon by the military engineers. The Great Oolite presents three 

 divisions constant in the Jura, but elsewhere artificial, and more distinct 

 in Ihoir mineral character than by their faunas. These are the Marnes a 

 Oslrca aciniiiiuda (M arnes vesuhennes of Marcou) ; the Great Oolite, 

 properly so called, and the Dalle nacree. The first is a blue marl, made 



