• MAUCH CHUNK OF THE ANTHRACITE COAL BASINS 459 



shales without having tlie attention called to the presence of mud-cracks, 

 even though the formation may in reality abound in them. 



The writer examined also the section from White Haven, on the 

 Upper Lehigh river, to Wilkes Barre, but the exposures were old and 

 those of shale not numerous, with the result that well defined mud-cracks 

 were noted at only one place. This was in the lower portion of the for- 

 mation, 3.5 miles north of White Haven, where the fresh waste rock 

 from the excavation of a cellar had been thrown two years previously 

 into the roadway. In this material numerous good examples of both 

 mud-cracks and rain-prints were found. Slabs bearing rain-prints were 

 also observed, however, on the road leading to the Wlrite Haven sana- 

 torium in the Upper Mauch Chunk, as well as at this other locality. 



These indications of exposure to the air during sedimentation were 

 found from 15 to 18 miles north of the present southeasternmost outcrop 

 at Mauch Chunk and in what is now on the strike of the central portion 

 of the iasin of deposition. That the basin was formerly much more 

 extensive is shown by the fact that the Mauch Chunk formation reaches 

 its greatest thickness in the region of the southern coal basin, but the 

 material is fine grained and not strikingly different from that farther 

 northwest. Considering its thickness of 3,000 feet, this outcrop must 

 have been at least a score of miles, and perhaps several times that dis- 

 tance, from the southeastern margin of the original basin. There is 

 nothing, in fact, save these marks of subaerial exposure to suggest the 

 proximity of such a shore as has been frequently postulated in order to 

 explain their presence. The results of these limited observations indi- 

 cate that further detailed search would doubtless yield, on other sections, 

 still more evidences of widespread mud-cracking. 



The Pottsville and White Haven sections further supplement each 

 other. At Pottsville the middle two-thirds of the Mauch Chunk were 

 well displayed and showed that the argillaceous strata were habitually 

 exposed to the air and well dried before being covered by the succeeding 

 stratum of sand. At White Haven evidences of subaerial exposure were 

 found in the lowest quarter and also in the uppermost quarter of the 

 formation. If it be not unwarranted to consider the evidence of the 

 one region as appl^ying also to the other, it may consequently be stated 

 that from the beginning to the end of the deposition of the Mauch Chunk 

 in the region of the southern and middle anthracite coal basins there is 

 inorganic evidence of a frequent exposure to the air following the laying 

 down of the argillaceous strata. Naturally in only a small per cent of 

 the beds would the evidence of such exposure be both preserved and 

 exposed. 



