MARYLAND GEOLOGICAL SURVEY 91 



saurian limb bone. This latter fossil, wliicli was found at the sur- 

 face of the formation, was much worn and may have been redeposited 

 from the Arundel. 



Strike. Dip, and Thickness. — The general strike of the Patapsco 

 corresponds practically to that of the formations which lie beneath 

 it. The normal dip of the basal beds is southeastward at the rate of 

 35 to 40 feet to the mile, but the dip, like that of the preceding 

 formations, increases toward the "Fall line." 



The thickness of the Patapsco is somewhat variable, gradually 

 increasing to the southeast. Within Prince George's County the out- 

 cropping thickness is about 100 feet. In some places, east of its 

 outcrop, the formation is estimated to have a thickness of about 200 

 feet. 



Stratigrapliic Belations.- — The Patapsco formation unconformably 

 overlies the Patuxent or the Arundel formation of the Potomac 

 group. It is overlain unconformably by the Raritan formation for 

 the most part, although here and there in the region of its outcrop 

 it is covered by Pleistocene deposits belonging to the Talbot or 

 Wicomico formations. 



The Upper Cretaceous Formations. 

 The Raritan Formation. 



The formation receives its name from Raritan River, ISTew Jersey, 

 in the basin of which it is typically developed. It includes the 

 deposits long called the Plastic or Amboy clays by the JSTew Jersey 

 Geological Survey. On the basis of the plant fossils, the formation 

 has been regarded as representing the Cenomanian series of Euro- 

 pean geologists. 



Areal Distribution. — In its wider distribution the Raritan fornui- 

 tion has been recognized from Raritan Bay, New Jersey, to the basin 

 of Potomac River. In the northwestern portion of the county it is 

 represented by a narrow outcrop which crosses the area in a sinuous 

 line from northeast to southwest and is also present near the head- 

 waters of some of the creeks along the western margin of the count v. 



