Appalachian Geosyncline. 241 



talline upland would, however, show a greater dominance of 

 granite or gneiss cobbles over those of vein quartz as compared 

 with gravels due to normal weathering and previously stored 

 by rivers in a piedmont slope. The character of the silt in the 

 two cases would also be different. Again, if vegetation had 

 not evolved to that state where, under a favoring climate, it 

 could bind the soil, a movement toward a cooler and wetter cli- 

 mate, even without glacial conditions, might lead to more rapid 

 instead of less rapid erosion of the uplands. In that case, how- 

 ever, coarse and fine detritus would both be carried to the 

 delta and clean formations of sand and gravel would not be 

 conspicuous. 



The more normal and probable relations of climatic fluctu- 

 ations to mountain, piedmont, and delta which were first stated 

 will be assumed to have existed during the later Paleozoic and 

 the justice of that assumption tested by the degree to which its 

 expected results accord with the observed stratigraphy of the 

 delta plain and shallow sea. If the theory that pulses in cli- 

 mate are recorded in sedimentation be regarded as sound, it 

 may then be used in two ways in the interpretation of the past: — 

 the deposits of an ancient delta may contain a climatic record 

 and at the same time testify to the former existence of a pied- 

 mont now destroyed as the result of orogenic movements and 

 later erosion. It is from this standpoint that the subject enters 

 into the present problem. 



The Catskill red shales and gray sandstones are succeeded by 

 the Pocono sandstones and conglomerates. The Pocono for- 

 mation spreads across the state of Pennsylvania, but the beds 

 in the east are coarser and thicker than farther west. Shale is 

 much diminished in amount. Most of it is olive, though, espe- 

 cially in the western half of the state, considerable red shale 

 occurs. Scanty coal seams show for their times and areas the 

 presence of perpetual swamps. This Pocono sandstone plate 

 is abruptly followed by the Mauch Chunk red shale and red 

 sandstone; brilliant with ferric oxide, containing lime, gypsum 

 and salt, with mud-cracked strata in place of coal. This for- 

 mation closed the Mississippian period. The Pennsylvanian 

 follows, inaugurated by the group of Pottsville conglomerates 

 and sandstones with black shales and some coal, reaching a 

 maximum thickness of about 1200 feet in Pennsylvania. This 

 is succeeded by the coal measures. The whole series from the 

 opening of the Middle Devonian reaches a maximum thickness 

 in Schuylkill County, Pennsylvania, of more than three miles. 



The red shale formations, the Catskill and Mauch Chunk, 

 show transitions on the east into the overlying formations. 

 The Pocono, on the contrary, passes abruptly at its top into the 

 Mauch Chunk shale. Both the Pocono and Pottsville conglom- 



Am. Jour. Sci.— Fourth Series, Vol. XXXVII, No. 219.— March, 1914. 

 18 



