48 PHYSICAL. GEOGRAPHY 



The black oxide of manganese occurs in the neighbourhood 

 of New Market; so that this portion of the Frederick-town 

 valley may be styled its metalliferous region. The limestone 

 in which the metallic veins are principally found is conti- 

 guous to a series of argillites, through which large bands of 

 quartz rock project perpendicularly, and having more effectu- 

 ally resisted the progress of disintegration in the whole mass, 

 form low unbroken walls, sometimes of considerable extent. 

 These slates belong to the series of primary rocks that extend 

 eastward to the tide-waters. 



Descending the valley, at the foot of the Catoctin there is 

 an extensive deposite of hasmatitic brown oxide of iron asso- 

 ciated with phosphate of iron, and a similar ore is found, 

 which was formerly abundantly raised, near the Point of 

 Rocks. At the Yellow springs, on the head waters of the 

 Tiiscarora, a deposite of black shale containing vegetable 

 matter, and overlaid by conformable beds of grey sandstone 

 were observed, which render the recurrence of bituminous 

 coal possible in this locality. Anthracite has certainly been 

 discovered on the Monocacy in. thin seams running through 

 the red sandstone. The capitol breccia again makes its 

 appearance west of Fredericktown, and continues protruding 

 itself in knolls, and forming the masses of a low range of 

 hills between the Catoctin mountain and the Monocacy, ex- 

 tending in a north-west and south-east direction across the 

 Potomac. At the foot of the south-western slope of the 

 Sugar-loaf mountain, quarries of coloured sandstone, and of a 

 beautiful white freestone, composed of grains of semi-trans- 

 parent quartz, cemented together by a talcose mineral, tra- 

 versed also by veins of crystallized quartz have been quar- 

 ried — the latter being the material of which the splendid 

 aqueduct over the Monocacy is constructed. 



Entering Montgomery county in this direction, the red 

 sandstones occasionally of light grayish red colour, continue 

 to make their appearance, and are extensively quarried near 

 the mouth of Seneca creek, where they envelope vegetable 

 remains, principally Calamines, and are occasionally traversed 

 by very slender veins of anthracite. They are succeeded by 

 argillites, and within a short distance of Rockville, the serpen- 

 tine formation containing beds of chromiferousiron is reached, 



