44:6 FOSSIL REMAINS OF LABYRINTHODON. [Ch. XXII. 



When Prof. Owen had satisfied himself, from an inspection of the 

 craninm, jaws, and teeth, that a gigantic Batrachian had existed at 

 the period of the Trias or Upper New Red Sandstone, he soon found, 

 from the examination of various bones derived from the same forma- 

 tion, that he could define three species of Labyrinthodon, and that in 

 this genus the hind extremities were much larger than the anterior 

 ones. This circumstance, coupled with the fact of the Labyrinthodon 

 having existed at the period when the Cheirotherium footsteps were 

 made, was the first step towards the identification of those tracks with 

 the newly-discovered Batrachian. It was at the same time observed 

 that the footmarks of Cheirotherium were more like those of toads 

 than of any other living animal; and, lastly, that the size of the three 

 species of Labyrinthodon corresponded with the size of three different 

 kinds of footprints which had already been supposed to belong to 

 three distinct Cheirotheria. It was moreover inferred, with confidence, 

 that the Labyrinthodon was an air-breathing reptile from the structure 

 of the nasal cavity, in which the posterior outlets were at the back 

 part of the mouth, instead of being directly under the anterior or ex- 

 ternal nostrils. It must have respired air after the manner of saurians, 

 and may therefore have imprinted on the shore those footsteps, which, 

 as we have seen, could not have originated from an animal walking 

 under water. 



But the structure of the foot is still wanting, and a more connected 

 and complete skeleton is required for demonstration ; for the circum- 

 stantial evidence above stated is not strong enough to produce in the 

 minds of some eminent anatomists the conviction that the Cheirotherium 

 and Labyrinthodon are one and the same. 



Dolomitic Conglomerate of Bristol. — Near Bristol, in Somersetshire, 

 and in other countries bordering the Severn, are certain strata which 

 rest unconformably upon the coal-measures, and consist of a conglom- 

 erate called " dolomitic," because the pebbles of older rocks contained 

 in it are cemented together by a red or yellow base of dolomite. This 

 conglomerate or breccia occurs in patches over the downs near Bristol, 

 and upon the flanks of the hills, filling up hollows and irregularities in 

 the Old Red Sandstone, Millstone Grit, and Mountain Limestone. 

 The imbedded fragments are both rounded and angular, and some of 

 them of vast size, especially those of millstone grit, weighing nearly a 

 ton. It is principally composed, at every spot of the debris, of those 

 rocks on which it immediately rests. At one point we find pieces of 

 coal-shakj in another of mountain limestone, recognizable by its 

 peculiar shells and zoophytes. Fractured bones, also, and teeth of 

 saurians of contemporaneous origin, are dispersed through some parts 

 of the breccia. 



These saurians are distinguished by having the teeth implanted 

 deeply in the jaw-bone, and in distinct sockets, instead of being solder- 

 ed, as in frogs, to a simple alveolar parapet. In the dolomitic con- 

 glomerate near Bristol the remains of species of two genera have been 





