244 GEOGNOSY OF THE APPALACHIANS. [XIII. 



quently met with in this series. The gneisses often pass into 

 schistose micaceous quartzites, and the argillites, which abound, 

 frequently assume a soft unctuous character, which has acquired 

 for them the name of talcose or nacreous slates, though analysis 

 shows them not to be magnesian, but to consist essentially of 

 a hydrous micaceous mineral allied to paragonite. They are 

 sometimes black and graphitic. 



III. The White Mountain Series. This series is character- 

 ized by the predominance of well-defined mica-schists interstrati- 

 fied with micaceous gneisses. These latter are ordinarily light 

 colored from the presence of white feldspar, and, though gener- 

 ally fine in texture, are sometimes coarse grained and porphy- 

 ritic. They are less strong and coherent than the gneisses of 

 the Laurentian, and pass, through the predominance of mica, 

 into mica-schists, which are themselves more or less tender and 

 friable, and present every variety, from a coarse gneiss-like 

 aggregate down to a fine-grained schist, which passes into ar- 

 gillite. The micaceous schists of this series are generally much 

 richer in mica than those of the preceding series, and often 

 contain a large proportion of well-defined crystalline tables 

 belonging to the species muscovite. The cleavage of these 

 micaceous schists is generally, if not always, coincident with 

 the bedding; but the plates of mica in the coarser-grained 

 varieties are often arranged at various angles to the cleavage 

 and bedding-plane, showing that they were developed after 

 sedimentation, by crystallization in the mass, a circumstance 

 which distinguishes them from rocks derived from the ruins of 

 these, which are met with in more recent series. The White 

 Mountain rocks also include beds of micaceous quartzite. The 

 basic silicates in this series are represented chiefly by dark- 

 colored gneisses and schists in which hornblende takes the 

 place of mica. These pass occasionally into beds of dark horn- 

 blende rock, sometimes holding garnets. Beds of crystalline 

 limestone occur in the schists of the White Mountain series, 

 and are sometimes accompanied by pyroxene, garnet, idocrase, 

 sphene, and graphite, as in the corresponding rocks of the 

 Laurentian, which this series, in its more gneissic portions, 



