Geology and Mineralogy. 547 



" The widespread horizontally of the Coal Measures deposits, 

 coarse and fine alike, recalls conditions observed on the Siberian 

 Steppe and other river regions. The folding of the beds pro- 

 ceeded from a common cause, lateral pressure applied at the east. 

 The violence of plication decreases with notable regularity toward 

 the west, until in western Pennsylvania and in Ohio, along a line 

 of more than 100 miles, the folds become so gentle that they can 

 be traced only by close study. Dips of more than one degree 

 are unusual, while at times and for considerable distances the dip 

 is barely one half of a degree. The same condition exists in a 

 great part of West Virginia. The regular decrease in steepness 

 of the folds leads to the belief that originally the beds were, to 

 all intents, horizontal throughout the basin, the condition being 

 that observed on the great river plains of comparable extent. 

 The rare occurrence of driftwood in the widespread deposits is 

 characteristic not only of the Coal Measures but also of vast river 

 deposits, those of the Amazon, as described by Brown, and of the 

 Ganges as described by Medlicott and Lyell. The long narrow 

 areas of coarse to pebbly sandstone, often with driftwood, recall 

 the tilled valleys of the Sierra, described by LeConte, as well as 

 tilled deserted bows on the Mississippi and the filled channels so 

 often disclosed when a stream in flood cuts across its 'bottom.' 

 The distinct evidence of sorting of materials in the red shales, 

 where clay and sand are in dovetailing lenses, as well as in some 

 conglomerates, where hardly enough fine material remains to bind 

 the pebbles, leaves little room for doubt that the work was done 

 by streams moving rapidly in some cases, slowly in others. The 

 pebbles are not flat, such as one may find on a shore, but oval or 

 sub-spherical, river pebbles, and their gradual decrease in size as 

 well as number in certain directions shows that the materials were 

 rehandled many times. The rounded pebbles of coal and carbo- 

 naceous shale prove equally with those of quartz and sandstone 

 that the deposits, whence they came, cropped out and were 

 exposed to attack by streams of water. The marine limestones, 

 with one exception, are in definite, long, narrow and compara- 

 tively insignificant areas, and pass, at the borders, where those 

 remain for observation, into sandstone, chert or shale, the condi- 

 tion being that of an estuary surrounded by lowland, whose rivers 

 bring a minimum of sediment. The shallowness of the water by 

 which sediment was distributed and the short duration of the 

 flooding are disclosed by wave marks, sun cracks and footprints of 

 animals, occurring at so many horizons, while the moderate depth 

 of the estuaries, in which limestone was formed, is apparent from 

 the shore conditions of the limestone. The testimony of the 

 fauna is confirmatoiy ; that life needed not deep water, for it per- 

 sisted to the very shore line in Ohio. Unconformability by ero- 

 sion or by overlap marks the contact of Pennsylvanian with the 

 underlying Mississippian in almost the whole basin, showing that 

 the great part was dry land. 



"The record appears to show that the Appalachian basin, 



