THE UPPER PAR EOZOIG PRORAS, THEIR SUCEESSION 
AND RANGE? 
DAVID WHITE 
VII 
CONTENTS 
STRATIGRAPHIC VALUE OF LAND PLANTS 
THE DEVONIAN FLORAS 
Middle Devonian 
Upper Devonian 
THE CARBONIFEROUS FLORAS 
Mississippian (‘‘ Lower Carboniferous’’) 
Pennsylvanian (‘‘ Upper Carboniferous’’) 
Westphalian (Pottsville and Allegheny) 
Stephanian (Conemaugh and Monongahela) 
Permian 
‘‘ PERMO-CARBONIFEROUS”’ CLIMATES 
STRATIGRAPHIC VALUE OF LAND PLANTS 
Diastrophism and floral changes.—The terrestrial plant is insepa- 
rably dependent on the conditions, not only of the soil and the water, 
but also of the air from which it derives an important part of its sub- 
stance. Any change, therefore, in the climatic, terrestrial, or water 
conditions of its environment directly affects the plant and causes 
morphologic changes to a greater or less degree, the greater plant 
variations corresponding usually to the greater environmental changes. 
_ The great floral revolutions of geologic history are connected with the 
great diastrophic movements. 
Sensitiveness oj land plants to complicated environment.—The land 
plant, being essentially without the power of locomotion except by 
accidental dispersion of its progeny, is most vitally susceptible to 
changes in composition, temperature, etc., of its environmental 
elements. Accordingly it constitutes a most sensitive indicator of 
changes in these elements. The more highly organized the type the 
greater, in general, is its value as evidence either for identity of 
t Published by permission of the director of the U. S. Geological Survey. 
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