PALEOZOIC FORMA TIONS OF MARYLAND 4 1 5 



which included the Niagara beds at its bottom/ Mr. Schuchert 

 also fully concurs in correlating these Maryland beds with the 

 Salina. 



DEVONIAN STRATA ^ 



Helderberg limestone. — The largest area covered by this for- 

 mation is in the central part of the county which it enters to 

 the north of Flintstone and then runs in a zigzag manner back 

 and forth until it leaves the county on the western side of Evitt's 

 Mountain. Another area follows Shriver Ridge and passes 

 through western Cumberland across the county. A third area 

 enters in the eastern part of Wills Creek valley and runs across 

 the county, keeping west of Wills Mountain, to Potomac Sta- 

 tion ; and, finally, to the southwest is the Fort Hill area, beween 

 Rawlings and Dawson. The best localities for studying this 

 formation are the Devil's Backbone, northwest of Cumberland ; 

 the cliff on the West Virginia side at Cedar Cliff and the Balti- 

 more and Ohio Railroad cut near Potomac Station. The lower 

 400 feet of the formation is composed of fairly thin-bedded 

 bluish-gray limestones, separate pieces of which have a metallic 

 ring when sharply hit. The more shaly layers contain fossils 

 among which are Tentaculites gyracantJms and Spirifer va7iuxemi, 

 characteristic species of the Tentaculite limestone in New York 

 with which this zone is correlated. 



Messrs. Clarke and Schuchert in their revised classification 

 revived Vanuxem's geographical name of Manlius limestone 

 for the paleontological one of Tentaculite limestone. 3 The 

 Maryland zone was put in the Helderbergian instead of the 

 Cayugan period because, as clearly stated by Dr. O'Harra, "the 

 lithological break between it and the Salina is very marked and 

 can be followed in the field .... while there is no lithological 

 break between the Tentaculite and Lower Pentamerus subforma- 

 tions, and the division for mapping purposes cannot be made 

 here."'' 



'Summary Description Geol. Pennsylvania, Vol. II, p. 839, 1892. 

 ^The Geological Survey of Maryland has followed Dr. Clarke and Mr. Schuchert 

 in referring the Helderbergian period to the Devonian system. 



3 Science, N. S., Vol. X, pp. 876, 877, 1899. '' Allegany county, p. 96. 



