white: relations between coal and petroleum 197 



pelic deposits have been altered. This relation has long been 

 recognized and is known to be regional in effect, though the 

 extent of the dynamic influences and the differences in the 

 dynamo-chemical results vary from one point to another within 

 the region. Coal appears to be more responsive to pressure 

 than are the environing strata. Its sensitiveness to dynamic 

 action makes it possible, through the changes in the fuel, to 

 recognize this action in regions where other indications are 

 obscure and difficult to detect. ^^ 



The explanation of the dynamic alteration of coals as the 

 result of thrust was long ago proposed and has been accepted 

 by most geologists, especially in America, though it has gained 

 fewer adherents in Europe, where the coal fields are smaller and 

 the strata of most of the basins containing higher rank coals 

 are folded and faulted. Anomalous variations in the carboni- 

 zation of the coals in folded and particularly in faulted strata, 

 and the presence of coal high in volatile matter near faults, 

 all of which at first seemed fatally opposed to thrust meta- 

 morphism as a hypothesis, have, on the contrary, been shown 

 to constitute essential proof of the validity of the theory. In 

 another place^^ I have shown that abnormally high percentages 

 of volatile matter sometimes found in coals lying in folds, and 

 generally to be observed near thrust-faults in coal fields, are 

 really due to compensation or neutralization of the thrust by 

 buckling of the beds and by the faults themselves. Through 

 the shortening of the crustal arc by folding or by over-thrust 

 of broken beds the stress is partially compensated and the coals 

 are enabled to escape the maximum pressure intensity. In the 

 regions of great coal alteration, the shortening by mere hori- 

 zontal compression, which gradually takes up the stress and 

 diminishes the pressure delivered at the far side of the arc, must 

 have been very considerable. 



It is probable that, except in cases approaching graphitiza- 

 tion, the temperatures of coal alteration were never so high as 

 those necessary to accomplish the earliest effects of metamorph- 

 ism generally recognized by geologists in other rocks; yet the 



'•- U. S. Geol. Survey, Bull. 150: 142-145. 1898. 

 1* Bureau of Mines, Bull. 38: 114-125. 1913. 



