Branner.J 340 [Feb . 19) 



hanna at Nanticoke through Newport creek and its tributaries. These 

 streams, especially two of the largest of thern, have, at some time in the 

 past, borne an important part in the transportation, modification and re- 

 arrangement of the drift material. Their influence at present, however, 

 is very insignificant as compared with what it doubtless was as the glacial 

 epoch drew to a close. 



The Surface Rocks. 



The exposed or surface rocks of this region include the Carboniferous 

 shales and sandstones, some of them easily decomposed, the Pottsville 

 conglomerate, the sub- carboniferous red shales, and the Pocono sand- 

 stones, while the Catskill shales and sandstones lie just beyond the border 

 of the basin. The Carboniferous shales are of various degrees of hard- 

 ness and resistance, spots here and there preserving the striae remarkably 

 well, while in other places the same beds have disintegrated two inches 

 or more below the polished surfaces that remain.* 



Many of the sandstones have decomposed so rapidly that it is a very 

 common thing to find surfaces that were once rounded, smoothed and 

 striated in the characteristic way, now preserving not a single line that 

 can be identified beyond doubt. But in some places, where these same 

 sandstones have been protected by a considerable layer — say two feet or 

 more — of drift, and only recently uncovered, the striae are still well pre- 

 served. 



As a rule, the Pottsville conglomerate preserves its ice record most 

 faithfully, and frequently, too, under adverse circumstances. Cropping 

 out around the border of the coal basin, and just inside of the mountains 

 that limit the valley, this formation lies a little below the crest of these 

 ranges, forming a continuous shoulder where the disintegration of the softer 

 rocks, both above and below, has exposed it to the weather along the 

 greater part of its outcrop. In many places this exposed rim has been so 

 thoroughly polished that it is next to impossible to determine the direction 

 of the striation. Indeed not a few of these highly polished rocks had to 

 be passed over, especially during the early part of my observations, with- 

 out my being able to detect a single well defined line, and not until 

 my work was about drawing to a close did I hit upon a method for detect- 

 ing the markings upon such surfaces.-)- 



*I would not be understood as implying here that two inches represent the 

 total general erosion that has taken place in this region since the glacial epoch. 

 In such places as the one referred to, the surfaces are comparatively well pre- 

 served, while there are others in which the rocks have flaked oil" to the depth 

 of many inches, or even feet, by the action of frost, and from which, of course, 

 all evidences of glaciation have long since disappeared. 



+ A thin covering of soil sometimes permits a slow disintegration of the con- 

 glomerate, which leaves a few of the quartz pebbles in their original position, 

 fast in the body of the rock, with their upper parts cut away and polished by 

 glacial action. Examination of these polished pebbles, under a lens of low 

 power, may slfow minute stria', but it more frequently happens that these 



