198 CLARK AND BIBBINS — GEOLOGY OF THE POTOMAC GROUP 



names " white " and " hone " ore are also locally used on account of its 

 color and fine grain. The ore which occurs in beds of comminuted 

 lignite is thoroughly charged by the same, which circumstance is be- 

 lieved to materially aid in its reduction. This variety is known as "char- 

 coal ore." Nodules of white ore weighing a ton are not uncommon, while 

 ledges of the same have been encountered which require blasting, and 

 when broken up have more than filled a railway car. 



Other varieties, known as u brown ore," " red ore," etcetera, occur 

 abundantly, often in the same beds with the white ore, from which they 

 are generally derived by alteration near the surface. Both the brown and 

 the white varieties include grades locally known as " velvet ore" from 

 their fine, smooth grain and the beautiful druses of minute crystals of 

 siderite and its derivatives which line the geodes and septarian nodules. 



The " red ores " are apt to occur in clays scant in vegetable matter. 

 These are used to some extent as pigments (Venetian red) and to impart 

 desired tints to bricks, etcetera. Red ocher or " keel " also occurs in this 

 formation, notably near the base, and yellow ocher to a less extent. 



The Arundel formation has been worked for iron ore more or less 

 continuously since the middle of the eighteenth century. A good part 

 of our Revolutionary ordnance was made of it. At the present time, 

 owing to the low price of iron, only a single furnace smelting Arundel 

 ore is in active operation, but in former years they were scattered all 

 along the belt from Bush river to Muirkirk, and their picturesque ruins 

 are seen at many points. 



The most prolific beds occur at Bush, Joppa, Stemmers run, Seven 

 Mile hill, Baltimore, Elkridge,. Hanover, Jessups, Annapolis Junction, 

 Patuxent neck, Contee, Muirkirk, and Branchville. The principal 

 workings at the present time are at Muirkirk, where the ore also is 

 smelted. 



The Arundel clays are extensively employed in the manufacture of 

 brick and terra cotta, and to some extent for cement, pottery, and mod- 

 eling. The supplies are inexhaustible, and they commonly lie conven- 

 iently for transportation either by land or water or both. 



PA TAPS CO FORMA TION 



Name and lithologic characters. — The Patapsco formation is so called 

 from its typical' occurrence in the valley of the Patapsco river. Its 

 deposits consist chiefly of highly colored and variegated clays which 

 grade over into or are interbedded with sandy clays, sand, and gravelly 

 sand. Its arenaceous materials, particularly those lying adjacent to 

 ferruginous clay beds, are often indurated, forming " pipe ore " or cor- 



