STRATIGRAPHY OF THE POTOMAC GROUP 487 
mates which were made of the thickness of the largest lenses 
observed render it probable that they attain at least 125 feet. 
‘Characteristic local sections—QOne of the best sections is 
found at Reynold’s Mine on Piney Run, Anne Arundel county, 
one mile south of Hanover. It occurs on the western flank of 
the so-called “Elk Ridge” in a heavy lense constituting its 
axis and largely conditioning its existence. The section at 
‘Reynold’s Mine is as follows: 
SECTION AT REYNOLD’S MINE, ANNE ARUNDEL COUNTY. 
Raritan. White and light brown sand and gravel containing 
crusts of iron-stone - - - - - =" Rov Oram, 
Patapsco. White, varigated argillaceous sands, “fuller’s earth,” 
clay and paint clay, with paint rock at the base; 
silicified coniferous and cycadean trunks. = PDOukt..OF1n- 
Ferruginous ledge, more or less conglomeritic —- o ft. 3 in. 
Arundel. Drab colored compact laminated clays containing 
beds of lignite and bearing fern impressions ; 
nodules, flakes and ledges of ‘ white ore,” slightly 
plant bearing - = - - - - - 70+ ft. 
Total thickness” - - - - - go ft. 3 in. 
Another important section is found at Muirkirk, Prince 
George’s county, where also the iron ore clays have been 
extensively worked for many years. The Muirkirk section 
exposed at the “‘Old Blue Bank” on the Tyson estate is as 
follows: 
SECTION OF ‘‘OLD BLUE BANK’ MUIRKIRK, PRINCE GEORGE'S 
COUNTY. 
Raritan. Sandy gravel’ - - - - - - - Bieceatdae, ober 
Patapsco. Mottled gravelly loam; silicified coniferous and cyca- 
dean trunks” - - - - - - - P22 afte 
Arundel. Massive blue clay containing ‘white ore;” bones of 
Dinusauria at base - - - - - = 4 QOVa TEE 
Highly lignitic lens with “charcoal ore”’ . - 20 2 Ett 
Tough, “dry,” blue clay with ‘“‘white ore” - - <a) Ge Pett 
Patuxent. White sand~ - - - - - - - - 1o-+ ft. 
Total thickness” - - . - - = OS tamte 
