GEOGNOSY AND GEOLOGY. 165 
feet ; its mountains may vary much in appearance according as one or the 
other rock species predominates. They are generally spherically convex, 
with irregular valleys and deep ravines; the protruding rocks have much 
similarity to those of the variegated sandstones. Ore veins have not as yet 
been found in the Keuper. The soil resulting from the weathering of the 
marls is of great fertility, owing to the amount of lime. Springs are not 
abundant. The Keuper is found in England, Germany, Lower Saxony, 
Thiiringia, Swabia, the Jura; also in France, Alsace, &c. 
Pi. 46, fig. 11, exhibits a section of the rock salt formation as it occurs in 
Wiirtemberg. The strata of the Vosges sandstone are mdicated by a@ and 
1, and those of the incumbent sandstone by 6 and 2. Then follows the 
muschelkalk, c, with the lower 3, the middle 4, and the upper division 5: 
upon these rests the Keuper, d, with its three subdivisions, 6, 7, and 8: the 
whole is covered by the lias. 
Fossits or THE Rock Satr Formation. The fossils characteristic of 
the individual groups and subdivisions have already been mentioned; it 
remains now to notice some of rare occurrence, worthy of remark on 
account of their paleontological significance. 
The fishes peculiar to the muschelkalk belong to the Hybodontes, a family 
of Plagiostomes, which enter here and pass off the stage in the chalk. 
They had bony spines in the dorsal fins, which are frequently well preserved. 
These ichthyodorulites have decided longitudinal grooves and two rows of 
strong serrations: Hybodus tenuis (pl. 40, fig. 4). 
The teeth of the Hybodontes have a central-larger lobe accompanied on 
each side by smaller decreasing ones, where covered by enamel they exhibit 
longitudinal grooves, the roots being broad and porous. The genus 
Placodus is peculiar, to the muschelkalk, in which only teeth and a few 
bones have been found. This genus is characterized by small, obtuse. 
conical intermaxillary teeth, and a vomer, with broad, much depressed dental 
plates. Pl. 40, fig. 5, represents an entire upper jaw with teeth and 
vomerine plates of Placodus andriani, found in the muschelkalk near 
Bamberg. Other remains are of Saurichthys mougeoti, &c. Rhomboidal 
scales of ganoid fishes, and especially Gyrolepis, are found in the 
muschelkalk: G. alberti, fig. 7°. 
The family of Labyrinthodonts, exhibiting relations to both Batrachia and 
crocodiles, is one cf exceeding interest to the zoologist. They possessed a 
rough, depressed skull, with long conical teeth implanted in distinct sockets. 
and some of the anterior developed into formidable tusks. The exterior of 
the tooth is longitudinally furrowed, and a transverse microscopical section 
exhibits the most complicated foldings of dental tissue. A somewhat similar 
structure of less complexity is found in Ichthyosaurus, and some of the 
recent species of Lepidosteus. Fig. 8, pl. 40, represents the skull of 
Mastodonsaurus jaegeri, a labyrinthodont found in the keuper: fig. 9: is a 
detached tooth, jig. 9 a transverse section of the same. 
Tracks of birds and of other less decided vertebrata have been found in 
the new red sandstone of Connecticut (pl. 41, fig. 32). Upwards of 70 species 
of such ichnites have been established by Hitchcock. Some of these tracks 
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