Maryland Geological Suevey 69 



lignites. Small deposits of pyrite are also found in the same beds. The 

 variegated clays which commonly exhibit a great variety of exception- 

 ally rich and delicate tints in irregular patterns often grade hori- 

 zontally into massive drab and black clays, which are often lignitic and 

 occasionally iron- or leaf-bearing. The sand sometimes contains pellets 

 or balls of white clay. They are frequently cross-bedded, although not 

 as strongly so as the sands in the Patuxent formation. Red ochre, known 

 as " paint rock " or " paint stone," occurs near the base and summit, 

 and sometimes within the formation, while flakes of sandy and ocherous 

 limonite with botryoidal inferior surfaces are not uncommon at certain 

 horizons. The variegated clays often contain small pieces of flattened 

 limonite quite uniform in size. The drab and chocolate-colored clays 

 have been worked at some points for iron carbonate in the Middle Eiver 

 region, but the amount of ironstone is small compared with that in the 

 Arundel formation. 



Steike, Dip, and Thickness. — The strike of the Patapsco formation 

 is essentially the same as that of the two preceding formations. The 

 direction changes slightly due to the structural features involved in the 

 central portion of the area by which the Patapsco formation gradually' 

 transgresses the earlier formations, both toM'-ard the north and toward 

 the south, which slightly affects the direction of the strike in the same 

 areas. 



^The dip is to the eastward at the rate of about 40 feet in the mile, 

 although it is somewhat increased within the Pall-line zone. The thick- 

 ness of the Patapsco formation is somewhat in excess of 200 feet, the 

 maximum thickness being observed in a well boring at Bowie, near 

 the Raritan-Patapsco contact, where a thickness of 260 feet was found. 

 The wells at Sparrows Point show a thickness of 204 feet, but it is pos- 

 sible that the upper beds had been eroded before the Pleistocene deposits 

 were laid down. At Eed Hill, Cecil County, a thickness of 130 feet has 

 been observed, while at Grays Hill, in the same county, it reaches 100 

 feet. 



