PATAPSCO AND RARITAN FORMATIONS 201 



Its variegated and drab clays, beside constituting vast supplies for the 

 manufacture of terra cotta, brick, etcetera, contain a few workable beds 

 of iron carbonate. The base of the formation is the principal source of 

 the well known Maryland " Venetian red " ocher, which also occurs 

 near its summit. There is a tradition among the inhabitants of the 

 Patapsco belt to the effect that this ocher was formerly used by the In- 

 dians for war paint. This rumor is substantiated by the fact that we 

 find on their deserted village sites cobbles of " paint rock," evidently 

 derived from the Potomac beds, which exhibit on their flat surfaces 

 numerous scratches which are clearly attributable to human agency. In 

 Cecil county the basal Patapsco clays, like those of the Patuxent, are 

 highly charged with diffused lignite and are employed to some extent 

 as a base for black pigments. In this area also the base of the formation 

 yields a fine, micaceous " fire " sand. 



RARITAN FORMATION 



Name and lithologic characters. — The Raritan formation receives its 

 name from the Raritan river, New Jersey, in the basin of which the de- 

 posits of this formation are typically developed. The name was given 

 by the senior author of this paper in the annual report of the state geol- 

 ogist of New Jersey for 1892, although the term " Raritan clays " had 

 been somewhat loosely applied to deposits of this age by earlier writers. 



In the case of the Patapsco formation it was shown that the argilla- 

 ceous character was the more prominent. In the Raritan the arena- 

 ceous features are emphasized. This is particularly true of the upper 

 portions of the terrane. The sands are often of very fine texture, and 

 when mixed with white clay are known as " fuller's earth." They oc- 

 casionally contain white clay pellets and balls, and are at times gravelly. 

 They are commonly white, but, particularly in the lower portions of the 

 formation, are often stained by iron oxides. A notable illustration of 

 such coloration occurs on the west shore of Elk neck near the meridian 

 of 76°. 



Induration of the sands by hydrous iron oxide is common, the result- 

 ing rock being either a very hard* tubular or corrugated iron stone often 

 having a metallic resonance, or a softer, evenly bedded, brown sand- 

 stone, suitable for building purposes. A well known illustration of the 

 former variety is the Black rocks of the Patapsco, while the latter is 

 quarried to some extent at Sandy Brae, in Cecil county. At times the 

 presence of a trace apparently of a vegetable oil imparts to the rock a brill- 

 iant iridescence. This feature is also well exhibited at the Black rocks. 



* The deserted village sites of the Patapsco Indians which lie within the Potomac belt have 

 yielded a number of arrow-points, spear-heads, and axes made of this rock. 



