OF MARYLAND. 



49 



being about the centre of a group of primary rocks, that occu- 

 py nearly the whole of Montgomery, the upper portions of 

 Anne Arundel, much the larger parts of Baltimore and Har- 

 ford counties, and crossing the Susquehanna a little above 

 Havre de Grace, form the substratum of the table land in the 

 upper districts of Cecil county. 



The rocks belonging to this group are principally the usual 

 granitic aggregates of primary formations, sucli as coarse, fine 

 grained, and porphyroidal granites, gneiss, hornblende rocks, 

 sienite, limestone, micaschist, serpentine, steatite, talcslate, 

 clay-slate and argillites, alternating with each other and pass- 

 ing into each other in such a way as to render it difficult to 

 affix specific names to their different mixtures. They afl"ord 

 in themselves most valuable materials that are employed in a 

 variety of ways for ornamental or useful purposes, and con- 

 tain, moreover, deposites of metals and other minerals that 

 furnish large supplies to the agricultural and manufacturing 

 industry of the state. Among the metals imbedded in them 

 are the chromiferous and titaniferous iron ores ; the former 

 more usually called chrome ores, being extensively employed 

 for the production of several articles used as pigments and 

 dyes; whilst the latter, when worked with other iron ores, 

 yield a large per centage of metal. The principal localities 

 of the titaniferous iron ores are in the upper parts of Harford 

 county, those of the chrome, are more numerous; the chief 

 localities being in the northern part of Cecil county, in Har- 

 ford county near Cooptown, in Baltimore county, at the 

 Bare hills, seven miles from the city of Baltimore, at Soldier's 

 Delight, seventeen miles distant, and in Montgomery county, 

 near Rockville. The latter ore invariably occurs in the ser- 

 pentine formation, which also furnishes silicates of magnesia, 

 that are manufactured on a large scale into the sulphate of 

 that earth, known as Epsom salts. Manganese ore occurs in 

 Montgomery county, near Mechanicsville ; sulphuret of mo- 

 lybdenum, graphite, sulphurets of lead and of zinc, have also 

 been discovered, but to what extent has not yet been deter- 

 mined. Kaolin, or porcelain clay, has been discovered in many 

 places, produced by the decomposition of the coarse grained 

 granite, which is very common among the primary rocks of 

 Maryland ; it occurs in Cecil, Harford and Baltimore counties, 

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