88 THE GEOLOGY OF PRIIs'CE GEORGE S COUXTY 



River. In its wider distribution the formation occupies a compara- 

 tively narrow, irregular and much interrupted belt extending from 

 Washington to Bush River, near the head of Chesapeake Bay. There 

 are also outliers of less importance to the north and south of the 

 general outcrop. At Capitol Hill, Washington, a well boring, after 

 passing through about 50 feet of Recent and Pleistocene materials, 

 penetrated lol feet of exceedingly tough drab and highly colored 

 ligniitic clays which apparently belong to the Arundel formation. 

 Beneath these clays the boring passed into the Patuxent sands and 

 gravels. Clays probably belonging to the Arundel formation were 

 encountered in an excavation for a deep sewer in the vicinity of 

 Anacostia bridge. 



Character of Materials. — The materials composing the Arundel 

 formation are diverse in lithologic character. They comprise large 

 and small lenses of drab and iron-stained clays which in many places 

 contain concretions, flakes or ledges of earthy iron carbonate and 

 cellular limonite. Iron pyrite and gypsum occur less commonly. 

 The clays may be either laminated, carrying more or less sand, or 

 massive, Avith surfaces exhibiting slickensides. Logs of lignite, 

 usually deposited in a horizontal position and greatly compressed, 

 are found embedded within the formation. These logs are in places 

 massed in well-defined beds of such thickness and extent as to be of 

 local use to the miners for fuel. Occasionally large stumps are dis- 

 covered standing buried in the position in which they grew, with the 

 roots and trunks fossilized by iron carbonate and iron sulphide. 

 Seeds of plants are found near some of these beds. Locally the clay 

 is charged with comminuted lignite, when it is termed "charcoal 

 clay" or "charcoal ore." Here and there this "charcoal clay" con- 

 tains fossil bones. JSTear Muirkirk, Hatcher obtained from it 

 dinosaurian and other organic remains. Where the Arundel forma- 

 tion has been exposed to the atmosphere the carbonate ores have at 

 some places changed to the hydrous oxides of iron to a considerable 

 depth. Where this has occurred, clays which were originally drab 

 colored have become red or variegated. Along the western margin 

 of the formation the materials become arenaceous and locally consist 

 of lenses of sand. 



