THE MICACEOUS SCHISTkS. HJ-j 



the area that we are obhged to hinit ourselves to descriptions of the 

 microscopical features of the specimens collected near the hordcrs of the 

 Algoukian sediments, and to content ourselves witli suooestions as to the 

 legitimate conclusions to be ilrawn from them. For this purpose we mav 

 divide the southern schists into the micaceous and the hornblendic varieties, 

 leaving the Palmer gneisses to he treated with the gneissoid granites. 



THK :micaceous schists. 



The micaceons schists include true mica-schists, consisting essentiallv 

 of (juartz and muscovite, or (|uartz and l)iotite; feldspathic mica-schists, 

 containing, in addition to quartz and biotite, a large (piantit^- of feldspar; 

 and hornblendic, micaceous schists, which differ from the feldspathic varie- 

 ties in possessing some green hornblende. These varieties grade into one 

 another insensibly, so that there is represented in hand specimens a com- 

 plete succession of tyi)es from the typical mica-schists to rocks that might 

 be called hornblende-mica-gneisses. Even in a single hand specimen the 

 alternate l)ands may consist of feldspathic and nonfeldspathic schists, or 

 of the latter and the hornblendic varieties. There is such an intimate rela- 

 tionship exhiliited l)etween all these rocks, when their thin sections are 

 examined under the microscope, that there can be no doubt as to their 

 genetic connection. The separation into classes is merely for convenience 

 in description. 



MT"S< l)VnE-.SCHISTS. 



The nmscovite-schists are rare. They are higlily foliated, silvery-gray 

 nx-ks, witli contorted folia. They are not so detinitely banded as are the 

 less markedly foliated rocks, tliough bands can still l)e detected in some 

 specimens. In general appearance they are typical mica-schists. 



Under the nneroscope their thin sections show only elongated (luartzes, 

 muscovite, biotite, limonite, a few grains of magnetite, and tiny plates of 

 hematite. The nuiscovite occurs as little lamina cutting through the quartz 

 grains and as long wisps between them. It is to the existence of these 

 long wi.sps and of the elongated quartzes that the schistositv of the rock 

 is due. The biotite, which is present in small quantities only, appears as 

 small l)rowii Hakes scattered through the quartzes. Some iiTegular areas 



