484 A. W. GRABAU— PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



Monroan of this region. Above the shales lies the Croasdale conglom- 

 erate and sandstone, between which and the Lower Monroe exists a pro- 

 nounced hiatus. This sandstone marks the return of the sea in Upper 

 Monroe time, the type of sedimentation being that of the Decker Ferry 

 or early Cobleskill. 



At the Susquehanna Gap in Blue Mountain the section is not well 

 enough exposed to give a complete succession. The "Clinton" or near- 

 shore phase of the Niagaran has here a thickness of 989 feet (Claypole). 

 It consists of soft shales, sandstones, and iron ores, a 2 -foot bed of the 

 latter being considered by Claypole the top of the formation. Beneath 

 this is a 5-foot bed of "sand rock." Both the sand rock and the overly- 

 ing ore bed carry Xiagaran fossils, Claypole having recorded Beyrichia 

 lata, Calymmene clintoni, and Ormoceras vertebratum Hall from them. 

 Overlying the upper ore bed are green shales and thin, hard limestone 

 bands containing some fossils, among which Claypole found Lingula 

 oblonga Conrad (= L. clintoni Vanuxem) and Beyrichia (Klwdenia) 

 notata Hall. These shales are succeeded by 400 feet of red shales, which 

 have been correlated with the Bloomsburg red shales of the region farther 

 north. The shale is on the whole very uniform and fine grained, show- 

 ing, as do most of the shales of this type, scattered green spots and occa- 

 sional green layers and seams. Fossils are absent from these beds except 

 in the upper part, where, as will be shown elsewhere, they were subse- 

 quently introduced. The series is succeeded disconformably by the Ham- 

 ilton (Marysville) sandstone, which will be more fully discussed in a 

 subsequent paper. 



Elsewhere in Perry County the red Bloomsburg shales are 700 feet 

 thick and are succeeded by 700 feet of variegated red and green shales. 

 Near the top of the variegated shales occurs the Bloomfield (Landis- 

 burg) sandstone member, a bed of soft, friable sandstone, varying in color 

 from dull reddish to greenish and in thickness from 10 to 40 feet. It 

 contains an abundance of Leperditia cf. alta, and has besides furnished 

 some interesting remains of a primitive fish and a fishlike Agantha. The 

 latter is Palaaspis americana Claypole and the fish is Onctius pennsyl- 

 vanicus Claypole. The nearest relative of the Pakeaspis is P. (Holaspis) 

 sericea Lankaster sp. from the Lower Old Eed sandstone of Monmouth- 

 shire, Scotland, from which the American species differs only in minor 

 particulars. Onclius pennsylv aniens, as represented by fin spines, is a 

 type known from the Siluric and the Devonic, occurring as low as the 

 Niagaran. 



The gray shales succeeding are 200 feet thick, and consist of soft argil- 



