410 The Upper Dkvoxi.vx Deposits of Maryland 



COERELATIOX OF THE UPPEE DEVONIAN ' 



The Upper Devonian strata of Marj'land consists of two types of sedi- 

 ments, a lower marine type termed the Jennings formation, and an upper 

 continental type called the Catskill formation. These formations will be 

 considered in the order of their deposition. 



The Jennings Formation 

 introductory 



Nature of the Problem. — The Jennings formation consists of inter- 

 bedded shales and sandstones 4000 to 4800 feet tliick in Maryland, the 

 study of which presents great difficulties. This is due in part to the 

 great variability in the composition of the sediments. Sandstones and 

 shales succeed each other at frequent intervals in vertical sequence, while 

 beds of sandstone that appear very massive at one locality may pass into 

 a series of sandstones and shales in a short distance on the strike and 

 these again into shales, or vice versa, rendering it very difficult to discover 

 persistent horizons in them. Although fossils are profuse in some strata 

 they are rare in others, wide intervals being nearly barren, necessitating 

 a careful search for the fossiliferous horizons. Finally, the beds are intri- 

 cately folded in the Appalachian structure, while the areas in which the 

 Jennings outcrops, are separated by others in which the strata have been 

 removed by erosion. These features, in addition to the problems pre- 

 sented by the contained faunas, unite to render the study of this forma- 

 tion most diflBcult. 



Method of Solution. — The foregoing facts have rendered it neces- 

 sary to make a detailed study of the sections of the Jennings tliroughout 

 the State.'' The method has been to investigate the sections exposed in 

 each of the detached areas of Jennings in Maryland and in adjoining 



^ Contributed by Charles K. Swartz. 



' Professor Prosser, who studied the Upper Devonian before the investiga- 

 tions of the writer were undertalten, describes a number of these sections 

 elsewhere in this volume. The author is greatly indebted to him for the 

 privilege of examining his results in advance of their publication. 



