MARYLAND GEOLOGICAL SURVEY 



143 



ever, these mines have decreased in importance, as most of them have 

 been unable to compete with the Lake Superior ores and at the present 

 time the only furnace using these ores is located at Muirkirk in the 

 northern part of the county. The numerous immense pits now filled 

 with water that can be seen in this region furnish evidence of the 

 large quantity of ore that has been removed though the present opera- 

 tions are rather small. 



The Muirkirk furnace has been in almost continuous use since 

 1847, and during that time has produced a great quantity of high- 

 grade pig iron. After having been closed three years it was re- 

 opened in May, 1909, and is now producing about 400 tons of pig 

 iron per month from about 1,200 tons of ore. 



The ore is primarily an iron carbonate ore, though much of it has 

 been altered to limonite or hematite near the surface. The oxidized 

 ore is commonly called brown ore, while the carbonate ore is called 

 white ore. The various stages of alteration can be readily seen in 

 many specimens that have a shell of limonite or hematite with a 

 central core of siderite. In other cases the alteration has affected 

 the whole mass and no iron carbonate remains. 



The ore occurs in the form of flattened irregular nodules arranged 

 in rather definite layers in compact plastic clay. In certain cases 

 the nodules are in close contact and there is a persistent band of iron 

 ore, but in other places considerable clay occurs between the ore 

 masses. In most mines there are several layers of the iron ore 

 separated by beds of clay of varying thickness. The ore layers are 

 seldom more than 12 to 14 inches thick. Where the ore is mainly 

 iron carbonate the color of the clay is generally buff to drab, but 

 where the ore has been oxidized the clay is colored red and yellow. 

 Considerable lignite is contained in the clays associated with the ore 

 and, in places, the ore itself contains pieces of lig-nite. Such ore is 

 usually discarded because of the iron pyrite which it is apt to con- 

 tain. It is well knowTi that lignite acts as a precipitating agent of 

 iron sulphide carried in solution and it is not uncommon to find 

 pieces of lignite coated with iron pyrite. 



The Arundel iron ore does not contain as high a percentage of 

 iron as many of the iron ores used in this country, the average ore 



