I 



MAUCH CHUNK OF THE ANTHRACITE COAL BASINS 453 



lower half of the Pottsville and upper transitional Mauch Chunl?: repre- 

 sent a time interval when not only sedimentation ceased over the greater 

 portion of the northeastern Appalachian basin and Mississippi valley, 

 but actual iiplift took place, or change in other conditions, such as rain- 

 fall, sufficient to result in widespread though not very deep erosion. 



THE MAUCH CHUNK OF THE ANTHRACITE COAL BASINS 



Stratigraphic characters. — The outcrops of the Mauch Chunk sur- 

 rounding the southern and middle anthracite coal basins offer favorable 

 opportunities for the study of the formation. In this region it is 

 observed to consist of red shales, often more or less sandy, and red sand- 

 stones, often highly argillaceous. Conglomerates are extremely rare, 

 except in the transition beds in the upper part of the formation, where 

 green shales in sparing amount may also be observed. Impure calcite 

 concretions in red, sandy shales occur scattered through much of the 

 formation, but especially the lower half. These concretions are usually 

 nodules from 1 to 2 inches in diameter, which may be so abundant 

 as to form an impiire limestone and are apt to be segregated in certain 

 laminae. 



The microscope shows the shales to contain more ferric oxide than the 

 sandstones, as would be expected from the usual association of ferric 

 oxide and clay except where reducing waters have leached out the iron. 

 The colors of the shales are, more accurately, bright brownish reds. 

 The sandstones vary from bro^^vnish red to grayish and reddish purple, 

 but usually possess a sufficient amount of ferric oxide to give them a 

 color tone approximating to that of the shales. There is, in fact, in the 

 formation as a whole a marked homogeneity of color. The purer sand- 

 stones are, however, in some places delicately banded in color, though 

 still massive in texture, due to very thin laiiiinae of sand not over a milli- 

 meter in thickness, being relatively free from clay, and consequently also 

 from iron. These make handsome building stones, being used for that 

 purpose in many of the finest buildings in the principal cities of the 

 region. Occasionally beds of gray or green shales may also be observed, 

 but not in the body of the formation in the areas of maximum sedi- 

 mentation. 



During the progress of the second geological survey of Pennsylvania, 

 Winslow recorded complete sections of the Mauch Chunk formation at 

 Mauch Chunk on the Lehigh river and at Solomons gap near Wilkes 

 Barre, 24 miles to the north.* These, being made by the same observer, 

 are valuable for illustrating the variations in the formation and are 



♦ Summary, final report, vol. 3, part i, 1895, pp. 1815, 1821. 



