THE FORMATIONS AND THEIR RELATIONS 191 



Group. Formation. Age. Origin. 



I Talbot ) 

 Columbia ] Wicomico J Pleistocene 



vv icomico | Pleistocene . ] f Marine, 



I Sunderland J - j Estuanne, 



' i and 



Laf ayette Pliocene . . . . j { Fluviatile. 



A( l uia • • Eocene Marine. 



or 



Matawan Cretaceous ....... Marine. 



f Raritan Cretaceous 1 



Potomac j Patapsco. . . . , « i 



j Arundel Jurassic (?) ' -Estuanne. 



LPatuxent " j 



Newa ; k * Triassic Estuarine and 



C 7 s c tal s line Algonkian (?) Sedimentary and 



PA TUXENT FORMA TION 



Name and hthologic characters. -The Patuxent formation receives its 

 name from the Patuxent river, in Maryland, in the basin of which the 

 deposits of this horizon were first recognized as an independent formation 

 and systematically studied. The deposits consist mainly of sands at 

 times quite jpure and gritty, but generally containing a considerable 

 amount of kaohmzed feldspar (known as arkose), whence Roger's name 

 leldspathic sandstone " for its indurated derivative. Brown loamy 

 sands are also common and are often indurated. Clay balls are at 

 times distributed through the arenaceous beds, which in places contain 

 lenses of gravel (plate 24, figure 1), sometimes with cobblestones several 

 inches in diameter. Frequently the sands pass either abruptly or grad- 

 ually over into sandy clays, and these in turn into more highly argilla- 

 ceous materials, which are commonly of light color, but at times become 

 lead-colored and lignitic and rarely iron-bearing. Massive red and vari- 

 egated clays also occur, but they are of minor importance. They often 

 bear a striking resemblance to certain of the crystalline residuals, from 

 which they are directly derived by redeposition. Those arenaceous 

 materials which chance to lie adjacent to ferruginous clays are not in- 

 frequently indurated by hydrous iron oxide, forming a characteristically 

 corrugated ferruginous sandstone (occasionally inclosing oolitic sand) 

 or conglomerate. The more arenaceous deposits are commonly cross- 

 bedded and exhibit evidence of rapid deposition under varying condi- 



tions. 



m tL M ,~ ; h h : rr^s: sssr- «^— — - - srk f „, 



