THE PENNSYLVANIAN PERIOD. 591 



and which attains the remarkable thickness of something like 11,000 

 feet. The system is remarkable because of its singular conglomerates, 

 some of which are of glacial origin. These will be referred to again 

 in connection with the Permian. 



South and Central America. — In South America, rocks of Late 

 (Upper) Carboniferous age are somewhat widely distributed, though 

 less so than those of the Devonian period. The system has wide dis- 

 tribution in the lower part of the basin of the Amazon, where it rests 

 on older formations unconformably, and is not generally coal-bearing. 

 In Central America, the same system is reported from Guatemala. 



THE LIFE OF THE PENNSYLVANIAN PERIOD. 



I. The Plant Life. 



With the opening of the Carboniferous period the supreme bio- 

 logical interest shifted from the sea to the land, and centered in the 

 vegetation and in the amphibians, the forerunners of the great line 

 of terrestrial vertebrates. The leading interest lay in the Coal flora, 

 and to that we turn at once. 



The Coal Flora. 



The Carboniferous vegetation was climacteric in two senses, which 

 combine to make it doubly interesting; it was climacteric in its preser- 

 vation, and it constituted a real climax in plant history. The con- 

 ditions that favored phenomenal preservation have already been set 

 forth. This extraordinary preservation has with little doubt given 

 the Coal flora a degree of prominence over the preceding and succeed- 

 ing floras that it did not altogether possess, and there is perhaps need 

 to be on guard against over-emphasis ; but it was really a great period 

 in the history of plant-life. The leading factor was the pteridophytes 

 which at this time reached their widest deployment, and the summit 

 level of their organization. Ancestral gymnosperms were present, 

 but they held a secondary though not unimportant place. The angio- 

 sperms, the present ruling type, had not yet appeared. The lower 

 groups are but feebly represented in the record. It is not certain 

 that there were any mosses or liverworts, though Renault, Zeiller, 

 and others think that mosses were probably present. There are good 

 theoretical grounds for believing that bacteria, fungi, and, in moist 



