ARUNDEL FORMATION 197 



time to time in Potomac literature. The Patuxentbeds have been desig- 

 nated as the " sandstone member " (Fontaine, McGee, and others), and 

 its superjacent deposit as the " clay member." Tyson indicated in a 

 general way. on his map the position of the " iron ore clays " of the 

 " upper oolite," the latter term evidently including everything in the 

 Potomac above the Patuxent formation, which that 'author designated 

 as the " lower oolite." 



At points where the Arundel terrane is wanting, as in Cecil county, 

 the tracing of the superior boundary of the Patuxent becomes more 

 difficult, since there is a closer similarity lithologicalty between the 

 Patuxent and the super-Arundel deposits than between the Patuxent 

 and the Arundel. This difficulty is increased in the area named by the 

 scarcity of organic remains. 



Areal distribution. — The outcrop of the Arundel formation in Maryland 

 occupies a comparatively narrow, irregular, and often interrupted belt 

 extending from the city of Washington to Bush river. A few isolated 

 areas of minor importance occur to the northward and to the southward 

 of these points. At a number of places, notably to the northward, it is 

 wanting in the sections, the deposits of the next higher horizon resting 

 directly upon the Patuxent formation. 



A very notable mass of exceedingly tough, drab, lignitic, and highly 

 colored clays, apparently referable to the Arundel, but evidently barren 

 of iron ore. constitutes the foundation of Capitol hill at Washington/ 

 A well boring, after passing through some 50 feet of recent and Pleisto- 

 cene materials, penetrates 131 feet of these clays into the Patuxent sand 

 and gravel. A great body of clays, apparently belonging to the same 

 formation, is now being encountered in a deep sewer in the vicinity of 

 Anacostia bridge. 



Characteristic local section. — A section exposed at the Timberneck iron 

 mine near Hanover is as follows : 



Feet 



Karitan 1. Reddish sands, at times gravelly, considerably indurated 12 



Patapsco 2. Red, white, and brown, more or less argillaceous sands, with clay 



pellets 20 



Arundel 3. Tough, drab, massive, pyritous clays bearing iron carbonate 100 



Patuxent 4. White clay, exposed in the bed of Licking run 5 



Total thickness 137 



Economic- products. — The best known economic product of the Arundel 

 terrane is iron ore, whence the name " iron ore clays " of Tyson. There 

 are several varieties of this, the best being an earthy spathic ore, occurring 

 in nodules, flakes, geodes, and layers. It is locally known as " steel ore," 

 on account of the exceptional toughness of the iron made from it. The 



