Maryland Geological Survey 375 



The thickness of the Jennings formation in this section has been 

 estimated sevcTal times and by different observers from which it appears 

 that 3800 feet is not far from the formation's thiclcness in Jennings 

 Run. 



Dr. O'Harra gave the tliiclvness of the zone in the Jennings overlying 

 the conglomerate of Jennings Run as " about 650 feet " ' and stated that 

 the thickness of the entire formation along Jennings Run " is thought to 

 be between 3500 and 4000 feet." " Professor Stevenson estimated the 

 thickness of the Portage and Chemung rocks near Saxton in the north- 

 eastern part of Bedford County, Pa., as " almost 3400 feet " ° to which 

 is to be added tlie 200 ± feet of Genesee shale* making a total thickness 

 for the rocks representing the Jennings formation of about 3G00 feet. 

 It will be observed that the thickness obtained by Professor Stevenson in 

 both Bedford and Fulton counties agrees very closely with the results in 

 Jennings Run. 



It is somewhat difficult to decide upon the line of division between the 

 Jennings and Catskill and perhaps in some respects a merging of the 

 colors representing the two formations at their junction would be the 

 more satisfactory way to map them. The lowest appearance of red or 

 brownish-red rocks, which has been used in some instances as the line of 

 division in areal work, is a very variable horizon as has been shown in the 

 accounts of various sections in Washington and Allegany counties. The 

 horizon of the highest fossils which has been taken for the line of division 

 between the two formations is about 550 feet above the grit and con- 

 glomerate which has already been described as exposed in the Jennings 

 Run highway cut. In regard to the lithology of the rocks there are 

 plenty of dark red to brownish-red sandstones and shales below the last 

 fossils but it is noticeable that above this horizon the rocks are of a 

 brighter red color and for nearly a thousand feet consist almost entirely 

 of red shales and sandstones. 



* Allegany Co., p. 107. 

 'Ibid.,v>. 108. 

 ' T-, p. 78. 

 *Ibicl., p. 82. 



