MINERALS OF MARYLAND. 109 



it constitutes the principal rock. It has hitherto furnished but 

 few species of minerals and none possessing much interest. 



Mica of course is abundant, and also 



Garnets^ 



SiauroHcle, and 



Cyanite. 



The most important localities of garnets have already been 

 mentioned ; the staurotide and cyanite are abundant, particu- 

 larly the former ; large crystals of each are common, but 

 mostly imperfect. 1 have a crystal of staurotide, 1 inch thick 

 and 3^ inches long. 



At Scott's mills, IS miles north from Baltimore, magnetic 

 oxide of iron is disseminated in large proportion in the mica- 

 slate, accompanied by cyanite. 



The primary limestone of this region occurs in tiie gneiss 

 and mica-slate, and at one place in hornblend rock; it most 

 usually constitutes the surface of the valleys and in no instance 

 forms a hill oi any magnitude. It frequently appears as a large 

 nest or isolated mass embraced by the other rocks. The most 

 important localities are from S to 20 miles north to west from 

 Baltimore, where it forms the surface of a number of valleys 

 which are mostly connected together. In some valleys where 

 stratification is visible, it is usually nearly horizontal and the 

 rock is very pure; in other places it is mixed with foreign 

 matters and passes into gneiss or chlorite-slate and is thrown 

 up and much confused. 



It varies in structure from very large crystalline grains of 

 pure carbonate of lime to a small grained saccharoidal appear- 

 ance, which latter kind is used extensively for architectural 

 purposes in Baltimore. 



Dolomite abounds in the limestone districts and passes into 

 compact magnesian limestone ; in one locality a large grained 

 variety, apparently pure, emits a very fetid odour when struck 

 or rubbed. 



The following mitierals occur in the limestone: — 



Quartz, in detached masses and opaque crystals, is often 

 disseminated. 



Fetid quartz also occurs in the limestone. 



Mica, in small spangles, in those limestones which appa- 

 rently pass into gneiss. 



