488 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



ever, carry an undoubted Upper Monroe fauna. This continues for a 

 considerable distance into the overlying limestone, which Ulrich classes 

 with the Helderbergian, but which shows a large percentage of late Mon- 

 roan species, and is better referred to the Siluric, even though a number 

 of Helderbergian species make their appearance. It is merely a case of 

 a Siluro-Devonic transition fauna. 



Farther west, near Cumberland, Maryland, the whole of the lower as 

 well as the upper Monroe is represented by limestones, which rest with a 

 strong evidence of disconformity on the Keefer sandstone, which in turn 

 lies disconformably on Magaran. It thus appears as if the southern 

 extent of these mid-Siluric red deposits did not reach the Maryland line, 

 where only the reworked sands occur, which were redeposited in the 

 encroaching Lower Monroan Sea. 



Other Salina beds of Pennsylvania. — It is more difficult to differentiate 

 the red deposits of Salina age from the underlying Clinton and overlying 

 Monroan in the counties west of the Front Eidge (Blue Mountain). 

 The Shawangnnk is wanting, not having been extended to this region, 

 but red shales abound. How much of these, however, are reworked Long- 

 wood, deposited during Monroan time, is not yet ascertained. The most 

 significant exposure of these beds is undoubtedly found in the Blooms- 

 burg anticline or Montours Biclge of Columbia and Montour counties, 

 where the series reaches the surface in a narrow, eroded anticline with 

 steeply dipping sides, the center of which exposes the Clinton formation. 



Besting on the upper olive brown shales, limy beds, and flaggy sand- 

 stones of the Clinton, we find the Bloomsburg red shale, about 440 feet 

 thick and best exposed in the gorge of Fishing Creek, behind the village 

 of Bloomsburg. The beds are dark red, very uniform, though occasion- 

 ally sandy, and marked with a few thin la} r ers of green, which apparently 

 show reduction of the iron. No fossils have ever been obtained from the 

 red shales, but from variegated shales near the top of the red beds I. C. 

 White reports a species of Lingula in considerable abundance near Chu- 

 losky furnace, on the eastern line of Northumberland County. Thus it 

 appears that the Monroan portion of the series must be carried down a 

 slight distance into the red beds.* 



Overlying the Bloomsburg red shale are 407 feet of greenish and gray 

 shales alternating with red shales, sometimes high in iron content (10 

 to 12 per cent) and with thin beds of magnesian limestone near the top. 

 This is the Middle Salinan series of I. C. White, but must be classed as 

 Lower Monroan. No fossils have yet been reported from this series. 



* These formations are now being studied by Ruth Raeder, candidate for Ph. D, in 

 Columbia University. 



