THE SURFACE OF THE GLOBE. 139 



species are found in the mines of Thuringia, in the midst of in- 

 numerable fishes of genera now unknown, but which, in their cor- 

 respondence with the genera of the present times, appear to have lived 

 in fresh water. 



We know that the monitors are also fresh-water animals. A little 

 higher is the limestone called Alpine, and above it the shelly lime- 

 stone, so rich in entrochites and encrinites, which forms the basis of a 

 great part of Germany and Lorraine. 



It has produced skeletons of a large sea tortoise, whose shells might 

 be from six to eight feet in length ; and those of another oviparous 

 quadruped of the lizard tribe, of great size, and with a sharp pointed 

 nose. 



Ascending through the sandstones, which only offer vegetable imprints 

 of lrjge arundinaeese, bamboos, palms, and other monocotyledonous 

 plants, we reach the different layers of the limestone called limestone 

 of Jura, because it forms the principal nucleus of this chain. 



Herein the class of reptiles developes itself fully, and manifests 

 itself in various forms, and of gigantic size. 



The middle part, composed of oolites and lias, or of grey limestone 

 with grypheae, has had in deposite the remains of two genera the most 

 extraordinary of all, which have united the characters of the class of 

 oviparous quadrupeds with the organs of motion similar to those of the 

 cetacea. 



The ichthyosaurus discovered by Sir Everard Home has the head 

 of a lizard, but extended into a pointed muzzle, armed with conical 

 and pointed teeth; enormous eyes, of which the scelerotica is 

 strengthened with a bony case ; a spine composed of flattened vertebrae, 

 like the pieces used at the game of draughts, and concave on both 

 sides like those of fishes ; the ribs slender, the sternum and shoulder- 

 bones like those of lizards and ornithorynchi ; the pelvis small and 

 weak; and four limbs, of which the humeri and femora are short and 

 thick, and the other bones flatter, and set nearer each other, like the 

 stones of a pavement, so as to compose, when enveloped in skin, 

 fins all in a piece, and scarcely able to be bent ; in a word, analogous, 

 both in its use and construction, to those of cetacea. These reptiles 

 lived in the sea ; on land they could at best only crawl along like seals ; 

 and at the same time they breathed elastic air. 



The remains of four species have been discovered. 

 That most extensively found (I. communis) has blunt conical teeth, 

 and is sometimes twenty feet long. 



The second (I pi city o don) at least as large, has compressed teeth, with 

 round and swelling roots. 



p2 



