XIII. ] GEOGNOSY OF THE APPALACHIANS. 245 



closely resembles, though apparently distinct geognostically. 

 The limestones are intimately associated with the highly mi- 

 caceous schists containing staurolite, aiidalusite, cyanite, and 

 garnet. These schists are sometimes highly plumbaginous, as 

 seen in the graphitic mica-schist holding garnets in Nelson, 

 New Hampshire, and that associated with cyanite in Cornwall, 

 Connecticut. To this third series of crystalline schists belong 

 the concretionary granitic veins abounding in beryl, tourma- 

 line, and lepidolite, and occasionally containing tinstone and 

 columbite. (See Granites and Granitic Vein-Stones, ante, pages 

 194-199.) Granitic veins in the Laurentian gneisses fre- 

 quently contain tourmaline, but have not, so far as yet known, 

 yielded the other mineral species just mentioned. 



Keeping in mind the characteristics of these three series, it 

 will be easy to trace them southward by the aid of the concise 

 and accurate descriptions which Professor H. D. Rogers has 

 given us of the rocks of Pennsylvania. In his report on the 

 geology of this State, he has distinguished three districts of 

 various crystalline schists, which are by him included together 

 under the name of gneissic or hypozoic rocks. Of these dis- 

 tricts, the most northern, or the South Mountain belt, to the 

 northwest of the Mesozoic basin, is said to be the continuation 

 of the Highlands of New York and New Jersey, which, cross- 

 ing the Delaware near Easton, is continued southward, through 

 Pennsylvania and Maryland, into Virginia, where it appears in 

 the Blue Ridge. The gneiss of this district in Pennsylvania 

 is described as differing considerably from that of the southern- 

 most district, being massive and granitoid, often hornblendic, 

 with much magnetic iron, but destitute of any considerable 

 beds of micaceous, talcose, or chloritic slate, which mark the 

 rocks of the southern district. These characters are sufficient 

 to show that the gneiss of this northern district is lithologi- 

 cally, as well as geognostically, identical with that of the 

 Highlands, and belongs, like it, to the Adirondack, or Lauren- 

 tian system of crystalline rocks. The gneiss of the middle 

 district of Pennsylvania, to the south of the Mesozoic, but 

 north of the Chester valley, is described by Rogers as resem- 



