366 The Upper Devonian Deposits of Maryland 



have a smootli fracture, breaking- directly across tlie quai-tz pebbles, while 

 others liave an irregular, rough surface. No jasper pebbles were seen in 

 the blocks and they do not closely resemble the conglomerate that occurs 

 in the vicinity of Oakland and Mountain Lake Park in Garrett County. 

 They do, however, more closely resemble the conglomerate found on Pea 

 Eidge at Mr. John Eobinsnn's in the eastern part of Garrett County. It 

 is evident that Dr. O'Harra correlated these conglomerate blocks with 

 the one of Jennings Run since he stated that " Eemnants of the same 

 conglomerate [Jennings Eun] are seen along the top of Polish Moun- 

 tain." ' Four and one-third miles farther north in Pennsylvania, Pro- 

 fessor Stevenson gave the following description of loose conglomerate 

 blocks found on Polish Mountain : 



" Fragments of the Chemung Conglomerate lie plentifully along the 

 crest of the ridge, but none was seen in place 



" There is some possibility that the conglomerate seen on the crest of 

 Polish Mountain may belong to the lower one, as the shales seen in the 

 valley bear little resemblance to those overlying the Upper Conglomerate; 

 and, moreover, contain many layers with Ambocoelia gregaria and im- 

 pressions of crinoid stems, such as ordinarily characterize the shales 

 holding the Lower Conglomerate." ' 



The Chemung rocks consist largely of greenish, argillaceous and 

 arenaceous shales with bands of greenish to greenish-gray sandstone. The 

 average dip of the Chemung on Polish Mountain is about 20° and the 

 distance from its base to the top of the point south of the ^STational 

 Eoad one-half mile. An estimate of the tliickness of the Chemung ex- 

 posed on the upper part of this mountain gave 1000 feet. 



Farther to the northeast Professor Stevenson in his " generalized 

 section for Fulton County," Pa., gave the thickness of the " Portage 

 flags " as MOO feet and the Chemnng as 2220 feet, making a thickness of 

 3620 feet to which is to be added the Genesee t^hale which Professor 

 Stevenson estimated to have a thickness of 200 ± feet near Saxton ' in 

 the northeastern part of Bedford County making a total thickness of 



' Allegany County, p. 107. 

 = T%p. 205. 

 = T=, p. 82. 



