240 PROCEEDINGS OF THE ACADEMY OP [1884. 



pressed either into close folds, or into broad or contracted 

 anticlinal or synclinal flexures. 



The Cretaceous. — Resting upon the eroded edge of the Azoic 

 rocks are successive series of plastic clays, sand marls and green- 

 sand, which foi'in quite uniform strata, dipping at a low angle to 

 the southeast. This belt, having a width of 18 miles, extends 

 from the hills to the latitude of Noxontown mill pond, just south 

 of Middletown. 



The Tertiary. — The Cretaceous is succeeded by a stratum of 

 white or lead-colored clay, having a thickness of 10 to 20 feet. 

 This continues as far south as Murderkill Creek, and from fossil- 

 iferous evidence, must be referred to the Miocene. 



South of Murderkill Creek, the Miocene is succeeded by 3 to 

 10 feet of light or dark blue clay, beneath which is a uniform 

 stratum of fine glass sand, of at least 40 feet in thickness. That, 

 all the State south of Murderkill is later Pliocene, I shall 

 endeavor to prove in a future paper upon the younger formation. 



All the beds of the Tertiary lie in a nearly horizontal posi- 

 tion, dipping at a still lower angle than the Cretaceous, and 

 probably unconformable to the same. 



The Quarternary. — Covering most of the foregoing formations, 

 and reaching up the flanks of the Azoic hills to the height of 200 

 feet or more above tide, is a layer of sand and gravel, which to 

 the north is of a coarse, red nature, and to the south is fine and 

 white. They are called the Delaware Gravels and Estuary Sands, 

 respectively. Along the river and bay shores is also the belt of 

 bog-clay, which is modern, and of more recent origin than the 

 gravels. Also upon the summits of the highest hills in the State 

 are solitary patches of gravel which are evidently older than the 

 continuous stratum to the south. This high-level gravel, in the 

 absence of proper data, has been problematically referred to the 

 Tertiary, and is known as Bryn Mawr gravel. 



The Crystalline Rocks. 

 Geographical Position. — Generally speaking, the southern line 

 of the Azoic rocks is the limit of the highlands, but in certain 

 places they extend well into more level regions. Beginning with 

 a point upon the Mar3^1and boundar}^, a little north of where the 

 latter is cut by the Mason and Dixon line, the limit of the rocks 

 runs in a northeast direction, cutting through the western end of 

 Newark, and following the northern boundary of the town. 



