246 GEOGNOSY OF THE APPALACHIANS. [XIII. 



bling that of the South Mountain, or northern district, and to 

 consist chiefly of white feldspathic and dark hornblendic gneiss, 

 with very little mica, and with crystalline limestones. 



The gneiss of the third or southern district (that lying to 

 the south of the Montgomery and Chester valleys) comes from 

 beneath the Mesozoic of New Jersey about six miles north- 

 east of Trenton, and, stretching southwestward, occupies the 

 southern border of Pennsylvania, extending into Delaware and 

 Maryland. It is subdivided by Eogers into three belts. The 

 first or most southern of these, passing through Philadelphia, 

 consists of alternations of dark hornblendic and highly mica- 

 ceous gneiss, with abundance of mica-slate, sometimes coarse 

 grained, and at other times so fine grained as to constitute a 

 soTt of whet-slate. To the northwestward the strata become 

 still more micaceous, with garnets and beds of hornblende 

 slate, till we reach the second subdivision, which consists of a 

 great belt of highly talcose and micaceous schists, with steatite 

 and serpentine, and is in its turn succeeded by a third narrow 

 belt, resembling the less micaceous members of the first or 

 southernmost subdivision. The micaceous schists of this re- 

 gion abound in staurolite, garnet, cyanite, and corundum, and 

 are traversed by numerous irregular granitic veins containing 

 beryl and tourmaline. All of these characters lead us to refer 

 the gneiss of this southern district to the third, or White 

 Mountain series, with the exception of the middle subdivision, 

 which presents the aspect of the second, or Green Mountain 

 series. 



Above the hypozoic gneisses Rogers has placed his azoic or 

 semi-metamorphic series, which is traceable from the vicinity 

 of Trenton to the Schuylkill, along the northern boundary of 

 the southern hypozoic gneiss district. This series is supposed 

 by Rogers to be an altered form of the primal sandstones and 

 slates, and is described as consisting of a feldspathic quartzite, 

 or eurite, containing in some cases porphyritic beds with crys- 

 tals of feldspar and hornblende, together with various crystal- 

 line schists ; including, in fact, the whole of the great serpentine 

 belt of Montgomery, Chester, and Lancaster Counties, with its 



