168 HISTORICAL GEOLOGY 



during the Pennsylvanian, the vulcanism probably being a con- 

 tinuation of that begun in the preceding period. 



Other Continents. — Much rock of Pennsylvanian age, both 

 of marine and non-marine origin, occurs in Asia, with coal beds 

 in Asia Minor, the east side of the Ural Mountains, and in northern 

 China. The coal beds of China are said to be extensive and 

 important. 



Marine strata without coal occur in northern Africa. In the 

 Zambesi district of southern Africa a coal field is known. 



In Australia and South America marine and non-marine strata 

 of this age are also pretty widespread. Much coal occurs in 

 southern Brazil. 



Climate 



Until comparatively recently the plant life of the great coal 

 period was thought to imply a warm to tropical, very moist, 

 uniform climate. More careful study, however, clearly points to 

 a temperate, only relatively humid, but remarkably uniform 

 climate. Some of the criteria favoring this latter view may be 

 stated as follows: 1 The great size and height of the plants 

 together with their frequent succulent nature and spongy leaves 

 indicate luxuriant growth in a moist, mild climate; absence of 

 annual rings of growth shows absence of distinct change of seasons; 

 the presence of aerial roots, by analogy with similar modern plants, 

 implies a moist and warm climate; the nearest present-day allies 

 of the coal plants attain greatest growth in warm and humid 

 climates; at present the greatest accumulations of vegetable 

 matter in bogs and marshes take place in temperate climates 

 where decay is not too rapid and thus suggests a similar climate 

 for the accumulation of the coal deposits; and the remarkable 

 distribution of almost identical plant types in Pennsylvanian 

 rocks from Arctic to tropical regions clearly shows a pronounced 

 uniformity of climate over the earth. 



Economic Products 



As already suggested, the principal economic product of Penn- 

 sylvanian age is coal, the richest and most extensive coal deposits 

 in the world being of this age. Eastern North America, western 



1 Based upon the work of D. White: Jour. Geol, Vol. 17, 1909, p. 338. 



