70 The Lower Devonian Deposits of Maryland 



horizon wliich is the probable equivalent of the American New Scotland 

 but may also include the Coeymans. Below this zone was said to occur 

 another member of the series, consisting of black flaggy limestones, with a 

 strange fauna, in the main unlike those above and below, and character- 

 ized by the peculiar gastropod Hercynella bohemica. It has now been 

 determined that, owing to widely dissimilar enviromnent, these two 

 Bohemian zones are different faunal and lithologic facies of one general 

 horizon. As far as known, there is no transition between the zones of E 

 representing the Silurian and those of F now placed at the base of the 

 Devonian. Further, the Bohemian Silurian and Devonian faunas are 

 derived from the southern or Mediterranean realm, while in northern 

 Europe the Silurian had its origin in another province and in addition all 

 was there land during the early stages of the Devonian. It probably is 

 more accurate to state that the basal Devonian strata of the Rhineland are 

 almost barren of marine life and that the little that has been discovered 

 may be as old as the Helderberg, yet no safe data are revealed on which 

 to base correlations between Europe and America. There is, therefore, 

 as yet no accepted European standard section that unmistakably indicates 

 the dividing line between the Silurian and the Devonian. In western 

 Maryland, however, a long complete section extends through the later 

 stages of the Silurian into the basal Devonian, but unfortunately all the 

 members of the former series have not yet yielded a characteristic marine 

 fauna. These beds, the Tonoloway and Wills Creek formations, do not 

 represent a normal marine habitat, but are rather derived from very 

 shallow seas accumulating both natural cement limestones and magnesian 

 limestones. Above the latter appears the Helderberg formation, which 

 at first is composed of nodular limestones (the Keyser member) which 

 are succeeded by shaly limestones and shales and these by heavier bedded 

 limestones. The lower strata of the Helderberg contain the earliest 

 normal marine fauna, not a large one, but varied enough when described 

 from the entire Appalachian region to be the basis for correlation. This 

 horizon appears to introduce a new diastrophic cycle in that it lays the 

 foundation for the great Devonian submergence of the North American 

 Continent. 



