Maryland Geological Survey 97 



but also the Tonoloway formation, the latter being considered equivalent 

 to the " Tentaculite " (Manlius) limestone of New York. Eowe divided 

 the Helderberg into the equivalents of the Manlius, Coeymans, New Scot- 

 land, and Becraft formations of New York. O'Harra' who prepared a 

 report upon the geology of Allegany County about the same time assigned 

 the same limits to it. Schuchert ^ made a critical study of the Lower 

 Devonian of Maryland a little later and published a brief synopsis of his 

 results in 1903. He divided the strata formerly embraced in the Lewis- 

 town formation as follows : 



.Becraft, 85-125 feet thick. Absent in western 

 Helderberg! Maryland. 



i New Scotland, 66 feet thick. 

 Coeymans, 110 feet thick. 



Manlius, 110 feet thick. 



Silurian Salina, 1135 feet thick. 



Niagara, 300 feet thick. 



The Helderberg, as defined by Eowe, is thus equivalent to the Helder- 

 berg, Manlius, and upper part of the Salina of Schuchert. 



In 1908-1909 Maynard ^ studied the beds termed the Manlius formation 

 by Schuchert (comprising most of the CJionetes jerseijensis zone). He 

 named them the Corrigan formation and correlated them with the Cobles- 

 kill, Eondout, and Manlius formations of New York and the Decker 

 Ferry, Eondout, and Manlius foi-mations of New Jersey, believing that 

 these units are undifferentiated in Maryland. 



In 1910 the writer proposed to the Committee on Formational Names 

 of the U. S. Geological Survey a further subdivision of these limestones. 

 In the following summer Ulrich, Stose and the writer visited western 

 Maryland together and agreed to divide the equivalents of the Lewistown 

 limestone into the Helderberg, Tonoloway, and Wills Creek formations 

 and assigned to them the limits recognized in this volume, in which con- 

 clusion Schuchert later concurred. The lower member of the Helder- 



^ Md. Geol. Survey, Allegany County, 1900, p. 94. 

 = Proc. U. S. Nat. Mus., vol. xxvi, 1903. 



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

 Hopkins University, 1909. 

 7 



