PALEOZOIC DELTA DEPOSITS 635 



formed, these being interpreted as flood plain and delta deposits. 

 ( Fraas-22 :5/(5) . The upper sandstone (Stnbensandstein) has been 

 interpreted as probably in part a fluviatile and in part an eolian 

 formation, the sandstones representing an accumulation on a flat 

 piedmont area at the foot of the actively eroded Vindelician moun- 

 tain chain. The extensive variegated clays of the Keuper have 

 been regarded by Lang and others as marine sediments, but 

 Philippi (44:4(55), Fraas (22:517), and Walther (58) consider 

 them rather as aerial sediments especially of eolian origin, repre- 

 senting a sort of loess-like accumulation. This interpretation is 

 suggested by the manner of occurrence in these sediments of the 

 skeletons of phytosaurians, aetosaurians, land turtles, and laby- 

 rinthodonts, with occasional dinosaurs, all lacking evidence of tran- 

 sport or destruction by aquatic animals such as might be expected if 

 the remains were carried into the sea. The prevailing color of 

 these sediments is red except where they were subsequently re- 

 worked by water, and here a gray color predominates. 



Paleozoic Delta Deposits. 



These are numerous, especially in North America, where a 

 whole series has been determined. Thus the entire Coal Measure 

 series and Permic of eastern North America chiefly consist of river 

 deposits with only occasional incursions of the sea. The Pottsville 

 conglomerate at the base of the series is an especially good ex- 

 ample. It was deposited from two centers, one in east central 

 Pennsylvania, the other in southern Virginia. From these points 

 outward the beds progressively overlap away from the source of 

 supply, and apparently upon an old land surface, there being in 

 these sections no marine equivalents. The Pocono sandstone is a 

 similar deposit, and between it and the Pottsville lies the Mauch 

 Chunk red shale, a deposit of river flood plain and eolian origin 

 during a period of relative aridity (Barrell-3). Still earlier in the 

 Devonic a similar deposit, the Catskill, was formed progressively 

 replacing a marine formation (Chemung) westward (Grabau-25). 

 The Oneonta (Portage) sandstone of New York and the upper 

 Hamilton or Ashokan formation is interpreted as of the same char- 

 acter. Still earlier in the Devonic the Esopus grit represents the 

 characters of a sea-level delta built westward by a stream debouch- 

 ing near northern Pennsylvania. The Gaspe sandstone of eastern 

 Canada likewise represents a Devonic dry delta deposit. vStill 

 earlier in the Siluric and Ordovicic similar dry deltas were built 



