I9II.] STEVENSON— FORMATION OF COAL BEDS. 33 



veys, he examined coal beds within a large part of the Appalachian 

 and Mississippi coal fields. His first report upon the work in Ken- 

 tucky is prefaced by discussion of matters relating to the origin of 

 coal beds as illustrated by conditions in the i\ppalachian basin. 



Bog plants are partially immersed and ordinarily are woody. 

 The trees are mostly resinous and are such as can thrive only in 

 bog conditions. The Coal Measures plants are ferns, clubmosses, 

 horsetails, reeds and rushes, in character much resembling the forms 

 prevailing in modern bogs. The peat of the Great Dismal and Alli- 

 gator swamps rests on white sand and fills the depressions, while 

 its surface is covered by canes, reeds and shrubs ; where there is 

 a cover of water, the soft black mud supports cypress and magnolia, 

 and a great mass of material is added each year. Some ponds were 

 once covered with vegetation, now sunken, as in Lake Drummond, 

 which has at its bottom a forest, probably carried down by its own 

 weight. He found similar phenomena in Sweden, Denmark and 

 Switzerland. The water, to permit formation of peat, must have a 

 constant level and be stagnant. The clayey bottom of bogs was 

 made by fresh-water mollusks and infusoria or by Characece and 

 Conferva:. Peat always has this mud. 



Comparing these conditions with those prevailing in the Coal 

 Measures, Lesquereux finds : ( i ) The fireclay varies in thickness, 

 color, composition and in the quantity of Stigjiiaria; sometimes no 

 coal rests on it — the soil was ready but conditions did not favor 

 accumulation. Yet fireclay, without coal at one place, is likely to 

 bear coal elsewhere. (2) The coal varies abruptly in physical and 

 chemical features, just as peat varies in all directions, horizontal and 

 vertical ; and these variations depend largely on the plants con- 

 cerned as well as on the amount of foreign matter introduced. (3) 

 The roof shales, usually very fine, are evidence of slow subsidence, 

 sometimes without marine invasion, as shown by plant remains: 

 sometimes with marine invasion, as where the shales contain shells 

 of brackish water type. (4) The limestones, equivalent to or con- 

 tinuation of the shales, need quiet deep seawater. Influence of the 

 sea is very distinct in erosions due to currents. (5) The sandstones 

 were due in many cases to turbulent waters, as appears from the 



PROC. AMER. PHIL. SOC, L, igSC, PRINTED .\PRIL 24, I911. 



33 



