RARITAN FORMATION 203 



The lignite of the Raritan is, as a rule, in a noticeably less advanced 

 stage of carbonization than that of the preceding terranes, being often of 

 brownish tint, and the logs somewhat less laterally compressed. 



The Raritan formation yielded the first American amber. Its original 

 source, cape Sable, on the Magothy river, was described in great detail 

 by Troost early in the last century. 



Organic remains. — The known flora of the Raritan formation includes 

 a thallophyte, a lycopod, ferns, conifers, cycads, monocotyledons, and 

 dicotyledons. No silicified stems or frond impressions of cycads have 

 been found in undoubted Raritan beds in Maryland, although certain 

 fronds have been reported by Newberry from the Amboy clays of New 

 Jersey. The endogenous element is weak and the exogenous particu- 

 larly prominent. There is a wide range of genera and species, with strong 

 modern affinities. 



The known fauna of the Raritan formation in Maryland is limited to 

 a single species of Teredo and possibly an insect. Borings of the former 

 are often met with in the trunks of lignitized conifers, so muoh more 

 commonly, in fact, than in the preceding formations as to suggest a 

 somewhat increased salinity of the Raritan waters. Four genera of 

 lamellibranchs are reported by Whitfield from the Raritan clays of New 

 Jersey, one with well marked Jurassic affinities. The clays of that area 

 are also reported by Cope to have yielded a pleseosaurian bone. 



The Patapsco- Raritan and Raritan- Mataioan boundaries. — Though at 

 times extremely obscure, owing to local similarities in litholog}^ the 

 Patapsco-Raritan line is not on the whole a very difficult one to trace. 

 The leaf beds, which are so much more common in the Upper than in 

 the Middle and Lower Potomac, are a great assistance with their 

 strongly exogenous and modern fades. 



The Raritan-Matawan boundary is not at all points as readily dis- 

 cernible as might be expected. The clay marls of the marine Creta- 

 ceous at times so closely resemble, the Raritan carbonaceous clays that 

 even the most careful observers have confused them. The well known 

 "black clays" of Grove point, Maryland, containing little or no glauco- 

 nite and much pyrite, have as often been referred to the Raritan as to 

 the Matawan and by equally careful observers. 



Areal distribution. — The outcrop of the Raritan formation in Maryland 

 occupies a crescentic and deeply dissected belt, often interrupted to the 

 landward, extending from the District of Columbia to the eastward of 

 Baltimore, across Elk neck to and beyond the Delaware border. Out- 

 crops occur along the " Eastern shore " as far southward as Fairlee creek. 



Characteristic local section. — The most comprehensive section of the 

 Raritan deposits of Maryland occurs at Giller's hole, Maulden moun- 

 tain, on the west shore of Elk neck. 



XXX— Bull. Geol. Soc. Am., Vol. 13, 1901 



