58 CARBONIGENOUS EKA. 



labyrinthodonts were at first thought to show affinities to the 

 batrachian order (frogs and toads), but were afterwards con- 

 sidered as members of the Saurian order, that of which 

 crocodiles and lizards are the modern representatives. They 

 were supposed to have been "Saurians arrested in their deve- 

 lopment, on the level of the batrachians," furnishing " a proof 

 that representatives of a permanent larva condition existed 

 among the loricated reptiles of the ancient world, in the like 

 manner as the sirens do among the recent batrachians." 1 

 [Latterly, Professor Owen has definitely placed the labyrintho- 

 donts amongst the batrachia, reckoning the archegosaurus as 

 in near alliance with the Proteus of our epoch, which is one of 

 the lowest of batrachian forms. 2 ] 



Coal strata are nearly confined to the group termed the 

 carboniferous formation. Thin beds are not unknown after- 

 wards, but they occur only as a rare exception. It is there- 

 fore thought that the most important of the conditions which 

 allowed of so abundant a terrestrial vegetation whatever 

 these were had ceased about the time when this formation 

 was completed. 



The termination of the carboniferous formation is marked in 

 some regions by symptoms of great disturbance. Coal-beds 

 generally lie in basins, as if following the curve of the bottom 

 of seas. There is no such, basin which is not broken up into 

 pieces, some of which have been tossed up on edge, others 

 allowed to sink, causing the ends of strata to be in some 

 instances many yards, and in a few, several hundred feet, 

 removed from the corresponding ends of neighbouring frag- 

 ments. These are held to be results of volcanic movements 

 below, the operation of which is further seen in numerous up- 

 bursts and intrusions of fireborn rock (trap). That these 

 disturbances took place about the close of the formation, and 

 not later, is shown in the fact of the next higher group of 

 strata being comparatively undisturbed. Other symptoms of 

 this time of violence are seen in the beds of conglomerate 

 which occur amongst the first strata above the coal. These, 

 as usual, consist of fragments of the elder rocks, more or 

 less worn from being tumbled about in agitated water, and 

 laid down in a mud paste, afterwards hardened. 3 It is to 



1 Quarterly Journal Geol. Soc. Nov. 1848. 



[ 2 Art. Palaeontology, Encyc. Brit. 1859.J 



3 It must at the same time be admitted that conglomerate is, in many 

 instances, simply a portion of the river alluvia of ancient times, ex- 

 actly resembling the gravel of our own era. 



