156 PROCEEDINGS OF THE PALEOXTOLOGICAL SOCIETY 



Although the field observations do not warrant an elaborate subdivision of 

 the series, it is possible to recognize two very distinct types of lithology in 

 the Maryland areas. The easternmost, which has been named the Taneytown 

 facies, is composed of gray, pink, and red, highly arkosic sandstones, in places 

 very micaceous. A coarse quartz conglomerate or a limestone conglomerate — ■ 

 the "Potomac Marble'' — lies at the base of the series, the quartz conglomerate 

 and the limestone conglomerate being generally mutually exclusive. The west- 

 ernmost, named the Emmitsburg facies. is predominantly soft red to purple 

 shale, weathering into cubes — in places micaceous. 



Conspicuous mud-cracks, vertebrate tracks, fragments of wood, together 

 with frequent cross-bedding, all point to continental conditions prevailing at 

 the time of accumulation of the sediments. Several diabase dikes, with a 

 general north-south direction, and one large sill, north of Emmitsburg, have 

 been intruded into the series. 



The structure of the red beds is a faulted monocline, with all dips north- 

 west and west, toward Catoctin and South Mountains. At one spot in Mary- 

 land a superb exposure shows conclusively that reverse faulting has occurred, 

 the west side showing relative upward movement. Once it can be proved that 

 there has been reverse faulting, there is no evidence to limit the amount. It 

 seems more rational, therefore, to assume an average thickness, say 5,000 feet, 

 and ascribe the great east-west development as due to duplication. If such 

 duplication has occurred, then the westernmost beds are not necessarily 

 younger than the eastern beds, but rather eastern and western beds are of 

 approximately the same age, differing only in character of sediments. Such is 

 thought to be the case, and is the reason for speaking of the Taneytown and 

 Emmitsburg facies rather than formations. It is also thought that the lime- 

 stone conglomerate occurring at the western boundary of the Newark, and in 

 New Jersey the heavy quartz conglomerate, are the same beds as those found 

 to the east and are basal. 



The red sandstones and shales are greatly jointed, in many places com- 

 pletely shattered to pieces. The strikes of the joints and faults are parallel, 

 or nearly so ; but since the faults are vertical and the joints are perpendicular 

 to the bedding, duplication did not occur by slipping along joint planes. 



The sequence of events which produced the Newark, as we have it today, 

 is thought to have been as follows : Briefly, the Appalachian area at the close 

 of Permian time was a region of crustal unrest — the forerunner of the later 

 uplift. Situated on this area of unrest a region of depression developed, in 

 which terrigenous red sediments slowly accumulated under true continental 

 conditions. At a late period in this deposition continual depression caused a 

 normal fault, which dropped the beds near their west side, causing the assump- 

 tion of west dip. 



At a subsequent time a radial thrust occurred, which was strongest in the 

 mountains on the west, and died out eastward. As the direction of this fault- 

 plane was parallel with the mountains, and also happened to be parallel with 

 the strike of the Newark rocks which formed in a basin whose long axis was 

 roughly parallel with the mountain axis, the vertical faults were strike-faults, 

 the type necessary to cause duplication of the red beds. The dikes of diabase, 

 where quarried, are vertical and are thought to have been intruded subsequent 

 to duplication. The crescentic shape of the ends of the contemporaneous basalt 

 sheets of New Jersey and Connecticut and of the intrusive sheets of Pennsyl- 



