96 



The Lower Devonian Deposits of Maryland 



S 







and nodular black chert and siliceous shale, with 

 a sparse fauna distinct from the Hipparionyx fauna 

 above and from the Helderberg below. 



In the eastern sections of Washington County, there is 

 no black chert, the time interval here being occupied 

 by the typical more sandy Oriskany. Near the base 

 are found Anoplotheca flabellites, Leptostrophia arcti- 

 muscula, and Ostracoda. Just below the middle occur 

 A. flabellites, Spirifer tribulis, 8. paucicostatus, 

 dance of ostracods and Chonetes hudsonicus. 

 Diaphorostoma desmatum. Near the top is an abun- 

 Pholidops multilamellosa, Tentaculites acula, and 

 Beachia suessana var. immatura, Anoplia nucleata. 



About 100 feet. 



CORRELATION OF THE LOWER DEVONIAN" ' 



The Helderberg Formation 



introductory 



Earlier students have held widely divergent views as to the limits and 

 correlation of the Helderberg of Maryland. It will be helpful therefore 

 to present a brief resume of the conclusions reached by them before dis- 

 cussing the problems to be considered. 



The Helderberg formation in Pennsylvania and Maryland is part of a 

 thick series of limestones to which Pratt ' gave the name Lewistown forma- 

 tion in 1881. This term was used in the reports of the Second Geological 

 Survey of Pennsylvania and also by the authors of several geological folios 

 of the U. S. Geological Survey." 



In 1899-1900 Rowe * made a critical study of the Lower Devonian of 

 Maryland and clearly recognized the complex character of the Lewistowm 

 formation. He separated it into three parts to which he gave the names 

 Niagara, Salina, and Helderberg formations. The Helderberg was made 

 to comprise not only the Helderberg formation as defined in this volume, 



' Contributed by C. K. Swartz. 



' Second Geol. Survey of Pa., vol. T, 1881, pp. 127-135. 



= Darton, N. H. Folios U. S. Geol. Survey Nos. 14, 1891, 32, 1894, 61, 1896, 

 Darton and Taff, Folio U. S. Geol. Survey No. 28, 1896. 



* Dissertation presented for the degree of Doctor of Philosophy in the Johns 

 Hopkins University, 1900. 



