INTERRELATIONS OF THE FOSSIL FUELS.* 



IV. 



By JOHN J. STEVENSON.. 



{Read March 5, 1920.) 



The Paleozoic Coals. 



In a great part of the areas, where deposits of Permo-Carbonif- 

 erous age are exposed, the passage f rum Triassic is gradual ; at 

 most, the plane of contact shows only petty discordance of stratifi- 

 cation. But in many extensive areas, the succession is incomplete 

 and one or more members are missing, so that the Triassic may rest 

 on any formation from Archean to Permian, In like manner, where 

 the succession is complete, the Permian may pass downward into 

 the distinctly Carboniferous so gradually that no definite boundary 

 can be determined stratigrap'hically or by aid of changes in plant or 

 animal life. At times, deposits assigned to the Permian rest on pre- 

 Carbonif erous rocks ; at others, there is distinct discordance be- 

 tween Permian and Carboniferous, while in vast areas the succession 

 is apparently conformable throughout. Lithological changes usually 

 occur in the upper part of the section ; at one time, the presence of 

 red rocks was considered proof that Permian had been reached. 

 This opinion is not final, in many regions red beds occur in distinctly 

 Carboniferous deposits. Frequently, the basal portion of the Per- 

 mian contains conglomerates, holding pebbles, striated seemingly by 

 glacial action. 



The problem of the relations between Permian and Carbonifer- 

 ous coal measures is vexatious to the last degree, as the testimony 

 of stratigraphy, paleontology and paleobotany seems to be in con- 

 flict. In some cases, the conflict is not real, but in others it is a 



* Part I appeared in these Proceedings, Vol. LV., pp. 21-203 .' Part II. in 

 Vol. LVL, pp. 53-151 ; Part III. in Vol. LVIL, pp. 1-48. 



405 



PROC. AMF.R. PHIL. SOC, VOL. LIX, Z, DEC. 20, I92O. 



