INTERPRETATION OF ENVIRONMENTAL CONDITIONS 201 



fauna whose elements occupied all the possibilities of the pool to preserve their 

 lives and propagate their kind, but there is an almost total lack of bizarre and 

 overspecialized forms, none heavily armored and none with an excessive develop- 

 ment of tusk or talon or spine, and none that could be called giants of their 

 kind. There was a full occupation of all the reasonable possibilities of life, but 

 nothing that would indicate an extreme adaptation, either for offense or defense, 

 to limited paths of life such as occur in other places and in other geological forma- 

 tions where the members of the faunas were very perfectly adjusted to each other. 

 There was only the healthy growth induced by competition in a fauna which still 

 retained all the resilience of its juvenile stage. 



"Such an assemblage existing under very powerful stress, if even from a single 

 source, was full of possibilities of development; ripe for the rapid and wide radia- 

 tion in habits and structures long denied them by the monotony of their environ- 

 ment. For the animals in such a pool there were but two possible endings. 

 Either the pool would become choked by the growing vegetation of the surround- 

 ing swamp, or in the many fluctuations of the land channels would open whereby 

 the animals could escape into other habitats and encounter a new environment. 

 It was apparently the first of these fates which came to the Lin ton fauna. It 

 was overcome in its full vigor before the ultimate adjustments of life to life had 

 produced the extreme development of armor and weapons of attack seen in more 

 mature or in senile faunas. Elsewhere in the same region similar faunas were 

 released to expend in morphological advances and various adaptations to new 

 conditions the stored-up stresses of similar periods of isolation." 



Studies similar to the one made upon the Linton fauna were made upon 

 the faunae found at Mazon Creek, Illinois, and at the Joggins quarries in 

 Nova Scotia. While they resulted in similar general conclusions, it was 

 impossible to determine the limits of the habitat and the life conditions so 

 closely. It is sufficient to say that from these three localities have come the 

 great majority of the known amphibian remains from the Pennsylvanian, 

 and all bear witness to the monotony of the environment and the accumu- 

 lating stresses which only awaited the great change of environment which 

 came with the advent of the red-bed conditions to burst into the great 

 radiation of reptilian and amphibian life of the late Paleozoic. 



In the report by Stevenson 1 on the Carboniferous beds of the Appalachian 

 Basin we have a summary of the conditions during the upper Paleozoic from 

 which parts are quoted: 



"The Allegheny is a thin formation, but its variations in thickness are con- 

 siderable. * * * There seems to be no reason for supposing that the Allegheny 

 becomes thicker southward in Kentucky, and at present there is little ground 

 for supposing that it ever reached much farther south than northern Tennessee. 



"The sandstones of the Allegheny contrast greatly with those of the Rock- 

 castle, even with those of the Beaver. They are persistent only as narrow bands, 

 and in any given area are apt to be replaced for considerable distances by sandy or 

 even clayey shale. Along the eastern outcrop from Kentucky northeastwardly 

 into Randolph and Upshur counties of West Virginia the sandstones are very 



1 Stevenson, J. J., Carboniferous of the Appalachian Basin, Bull. Geol. Soc. Amer., vol. 18, 

 p. 150, 1907. 



