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a frequent exposure to the atmosphere. One weakness, among others, 

 of the resulting hypothesis lies of course in the contradiction of modern 

 with geological evidence, which shows that abundant muddy sediments 

 are favorite haunts for certain kinds of marine organisms. 



Lesley states, in summing up his conclusions on the origin of the 

 Mauch Chunk after a lifetime of study on the Paleozoic formations of 

 Pennsjdvania, that — 



"It is astonisbing to see the great green and gray cross-bedded sandstone of 

 the Poeono age immediately followed by an equally great thickness of fine red 

 and reddish muds deposited in layers sometimes as thin as paper, sometimes 

 mixed with fine red sand, and showing so extreme a shallowness of the water 

 that the foot-tracks of lizards, rain-drops, and shrinkage cracks produced by 

 the heat of the sun have been retained between the layers. This shallowing 

 of the sea along what was undoubtedly a broad and low-lying shore receives 

 additional evidence from the occurrence of several small coal beds and several 

 small layers of iron ore at the top of the formation, the coal layers sometimes 

 being consolidated into a thin, workable coal bed, and the series of thin, solid 

 or nodular iron ore layers turning in places into solid beds of carbonate of 

 iron 4 feet thick, as at Ralston, Queens run, etc., or multiplied and made 

 economically valuable for furnace use, as on the west side of Chestnut ridge, 

 in Fayette county. 



"The surprise of the field geologist is renewed by observing this great red 

 shale formation immediately succeeded by the great basal conglomerate (Potts- 

 ville No. XII) of the lower productive coal measures. ... No disturbance 

 from folding or uplifting of the red shale before the laying down or coming in 

 of the conglomerate is anywhere visible, and I can suggest, after many years 

 of study, no explanation of the phenomenon. Others may be more successful ; 

 but lip to the present moment I look upon this as one of the many unsolved 

 problems in our geology, waiting not so much for more facts as for a shrewder 

 and more fortunate suggestion. I think no one can doubt that the red shale 

 was deposited on a broad shore-bordered lowland near the sealevel, and in 

 regions of its wide extent occupied by marshes, pools, and lagoons on which 

 the first true coal vegetation began to grow, and that in connection with this 

 vegetation considerable deposits of carbonate of iron, or of limonite afterwards 

 carbonized, were formed."* 



It is seen from the above that Lesley recognizes the one problem, that 

 offered by the contrast of the Mauch Chunk with the preceding and 

 succeeding formations, and also the second problem, that given by the 

 evidences of shallow water and occasional exposure to the atmosphere. 

 While not professing to understand it, he states the conclusion that 

 "the red shale was deposited on a broad shore-bordered lowland near 

 the sealevel." Thus he practically reaches a belief in its origin as a 

 river deposit marginal to the sea, but without specifically calling it a 



* Second Geological Survey of Pennsylvania. Summary, vol. iii, part i, 1895, pp. 

 1806-1807. 



