84 The Lower Devonian Deposits of Maryland 



STEATIGEAPHIC AND PALEONTOLOGIC CHARACTERISTICS' 



The Lower Devonian of Maryland is divided into the Helderberg and 

 Oriskany formations, which will be considered in the order of their 

 deposition. 



The Helderberg Formation 

 introductory 



The Helderberg is essentially a limestone formation. Its lithological 

 character varies not only in its ditferent beds but also in the exposures of 

 different regions. It ranges in color from dark blue to light gray, and in 

 texture from a massive limestone to a calcareous shale. Interbedded with 

 the limestone are numerous layers of black or white chert which occur at 

 various horizons. A single bed of white quartzitic sandstone about 10 

 feet thick is present in it on Elbow Ridge, northeast of Hancock, while a 

 gray argillaceous shale, 14 to 20 feet thick and free from calcareous matter, 

 except fossils, occurs at its top in the Cumberland region. 



The thickness of the Helderberg varies from 290 feet in the vicinity of 

 Hancock to about 350 feet in the Cumberland area. 



SUBDIVISIONS 



The Helderberg formation is divisible into four members which are 

 distinguishable both lithologically and faunally. Their sequence and 

 diagnostic features may be summarized as follows : 



'Contributed by Charles K. Swartz, T. Poole Maynard, and R. B. Rowe. 

 The Helderberg was first studied by R. B. Rowe who presented a discussion of 

 the Lower Devonian of Maryland as a dissertation for the degree of Doctor of 

 Philosophy in the Johns Hopkins University in 1900. This dissertation was 

 intended for publication in this volume. The work was revised by Charles 

 Schuchert in the course of his more extended studies of these strata. 



The lower part of the Keyser member of the Helderberg was studied by T. 

 Poole Maynard who offered a dissertation to the Johns Hopkins University for 

 the degree of Doctor of Philosophy in 1909 in which he discussed the strati- 

 graphy and paleontology of these beds. The work of these authors was 

 revised and much of it rewritten by C. K. Swartz as a result of his later 

 investigations. The discussion of the Keyser member of the Helderberg is 

 based chiefly upon the investigations of C. K. Swartz and T. Poole Maynard. 

 The remainder of the chapter is based upon the studies of Charles Schuchert, 

 C. K. Swartz and R. B. Rowe. 



