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GEOLOGICAL MEMOIRS. 



pied by the Trigonia navis, hitherto only found in Alsace, Swabia, 

 and Franconia. The family of the falciferi, which made its appear- 

 ance in the Jurensis-hed, is likewise represented in the German 

 species of Am. opalinus, Xtein. (Am. ammonius, Schl.), the constant 

 companion of Trig, navis, which always appears and disappears with 

 it. Together with Am. lineati, which in this stratum are usually 

 reticulate (Am. hircinus, Am. torulosus), are also found Belemnites 

 compressus, B. clavatus, and herds of Nucula Hammeri, N. clavi- 

 formis, Astarte, and small Gasteropoda. As a parallel to this bed, 

 so peculiar to the German gulf or bay, there now appears in France 

 and England the uppermost bed of their upper Lias, in which Am. 

 radians, the reticulate lineati, Nuculce, and Gasteropoda occur ; 

 immediately above these appear the sandstones, chiefly oolitic. 



The ferruginous sandstones have a very close connection with the 

 opalinus-cl&ys. They are likewise local littoral formations, which, 

 however, extend somewhat farther than the clays. A distinct boun- 

 dary between a. and (3. cannot be pointed out in Swabia ; fine and 

 unctuous below, the clays become farther upwards more micaceous 

 and sandy, until they form true sandstones alternating with clay beds. 

 They are characterized by Am. Murchisonce, Am. discus, Pecten per- 

 sona tus, Gryphoea calceola, and Gervillia. In the north-east of 

 Swabia we mid iron-ore beds in these sandstones ; iron is indeed 

 found more or less wherever they appear ; and hence the rock derives 

 its peculiar brown colour. The thickness of this formation increases 

 in the Kocher valley to 300 feet, but decreases more and more to- 

 wards the south-west ; near the Wutach, where the bed once more 

 assumes its full development, in Switzerland (Berne, Basle, Solothurn, 

 Aargau), where the fossils are less frequent, it has less thickness and 

 forms an alternation of arenaceous clay beds and sandstones, which 

 towards the top pass into hard limestone beds. This is termed by 

 the geologists of Mont Jura Oolite ferrugineuse ; but by this is 

 meant only the sand-beds, with Am. Murchisonce and Nautilus line- 

 atus ; the sandy clays lying on the top of the Jui*ensis-be& (Marnes 

 h Trochus) are called by them Gres superliasique, on the grey sandy 

 laminae of which remains of Asterias are remarkably abundant. This 

 Gres superliasique is also found in Burgundy (Vassy), where, how- 

 ever, the arenaceous beds begin to disappear. This is completely 

 the case at Calvados and in the south of England, where the so-called 

 Inferior Oolite lies immediately on the top of the radians-he&s, and 

 contains in the harder limestones of its lower portions Am. Murchisonce, 

 Am. Edouardianus, D'Orb, Am. Tessonianus, D'Orb., and Nautilus 

 lineatus. To the north of Bath sandstones reappear ; in part, as 

 great local formations, as at Northampton and Cheltenham (Cross- 

 hands), which are known as inferior oolite. These formations change 

 from the coarsely oolitic character through all shades to the finest 

 sand, sometimes brown and ferruginous, sometimes white with yellow 

 bands (Arbury Hill). Am. Murchisonce is certainly wanting, but 

 Pecten personatus, Clypeus sinuatus, Pholadomya obtusa, and others 

 are chiefly found. 



Thus there re-occur here, at the beginning of the "brown Jura," 

 conditions similar to those with which the "black Jura" commenced; 



