MINERALS OF MARYLAND. 107 



because their edges show portions of the faces of symmetric 

 crystals; their form is just what it would he if a perfect 

 crystal were cut by tlie lapidary on any two opposite sides until 

 it was very thin. 



Garnets occur sparingly in the granite and gneiss, but 

 abound in the mica-slates, some of which contain so large a 

 proportion and are of such an extent that the aggregate de- 

 serves a specific name. Near the Gunpowder river, 14 to IG 

 miles north-north-east of Baltimore, this garnetiferous mica- 

 slate may be traced for two or three miles. 



The forms are (primiiif and trapezoidal) of Hauy, and the 

 prismatic or elongated primitive crystals. Garnets of a large 

 size occur in a disintegrating mica-slate, 3 miles east of the 

 Gunpowder, frequently two inches in diameter; but they are 

 very ferruginous and opaque. 



Tourmaline of the common variety occurs in the granite, 

 gneiss, and mica-slate, and occasionally fine specimens are 

 obtained. The yellow and brown varieties occur in the lime- 

 stone. 



Sp/icne is sparingly disseminated in souk; of the Fatapsco 

 granite. 



Beri/l has been found in the granite and in the granite veins 

 of the gneiss, in large crystals. 



Phosphate of lime occurs in similar situations. 



Sulphuret of iron rarely occurs in the granite, but more 

 frequently in the gneiss, and presents many varieties of crys- 

 talline forms. 



Pyritous copper exists in small isolated grains in the 

 granite and hornblend rocks on the Fatapsco. 



Of the minerals hitherto noticed in the granite, all except 

 the sphene also occur in the gneiss. And there are many 

 others in the latter rock which have not yet been seen in 

 the Maryland granites. One of the most interesting localities 

 in the gneiss is about 1| mile from Baltimore, on Jones' falls, 

 where Dr. Hayden first noticed the following Uiinerals. 



Chabazie, (primitif) or Haydenite. 



Zeolite^ (pyramidal) and radiated. 



Sulphate of baryta^ (form indeterminate.) 



Sulphuret of iron ^ in crystals of divers forms. 



Carbonate of iron ^ (lenticular.) 



