The Rivers and Valleys of Pennsylvania. 195 



mass could have been so deeply worn off of the Newark belt 

 between the making of the last of the coal beds and the first of 

 the Newark. It seems more in accordance with the facts here 

 recounted and with the teachings of geological history in general 

 to suppose, as we have here, that something of the present 

 deformation of the ancient rocks underlying the Newark beds 

 was given at an early date, such as that of the Green Mountain 

 growth ; and that a certain amount of the erosion of the folded 

 beds was thus made possible in middle Paleozoic time ; then 

 again at some later date, as Permian, a second period of mountain 

 growth arrived, and further folding was effected, and after this 

 came deeper erosion ; thus dividing the destructive work that 

 was done into several parts, instead of crowding it all into the 

 post-Carboniferous time ordinarily assigned to it. It is indeed 

 not impossible that an important share of what we have called 

 the Permian deformation was, as above suggested, accomplished 

 in the southeastern part of the State while the coal beds were yet 

 forming in the west ; many grains of sand in the sandstones of 

 the Coal Measures may have had several temporary halts in other 

 sandstone beds between the time of their first erosion from the 

 Archean rocks and the much later time when they found the 

 resting place that they now occupy.* 



9. Neioarh deposition. — After the great Paleozoic and Perm- 

 Triassic erosions thus indicated, when the southeastern area of 

 ancient mountains had been well worn down and the Permian 

 folds of the central district had acquired a well developed 

 drainage, there appeared an opportunity for local deposition in 

 the slow depression of a northeast-southwest belt of the deeply 

 wasted land, across the southeastern part of the State ; and into 

 this trough-like depression, the waste from the adjacent areas on 

 either side was carried, building the Newark formation. This 

 may be referred to as the Newark or Trias-Jurassic period of 

 deposition. The volume of this formation is unknown, as its 

 thickness and original area are still undetermined ; but it is 

 pretty surely of many thousand feet in vertical measure, and its 

 original area may have been easily a fifth or a quarter in excess 

 of its present area, if not larger yet. So great a local accumula- 

 tion seems to indicate that while the belt of deposition was 



* These considerations may have value in showing that the time in 

 which the lateral crushing of the Appalachians was accomplished was 

 not so brief as is stated by Reade in a recent article in the American 

 Geologist, iii, 1889, 106. 



