THE SOUTHERN COMPLEX. 125 



Still further, it has been seen that the syenites in the same exposure 

 vary into syenite-schists; it has ])een seen that the granites vary into 

 granitoid gneisses; and the nature of the miiu-ral clianges wliich explain 

 this variation has been given. The coarser grained syenite-schists are 

 found, by examining thein in tliin section, to liave a background composed 

 of closely interlocking felds})ar precisely like the massive syenites. The 

 foliation of these rocks is due to the biotite and hornblende. Tlie large 

 blades of these minerals, arranged with their axes in a, common direction, 

 are within the feldspars, many l)lades often being included within a single 

 individual of that mineral. The relation is such in many cases as to make 

 it almost certain that these minerals have developed within the feldspar as 

 secondary products. The pressm-e to which the rocks were doubtless suli- 

 ject during the time of the growth of these minerals jjrobably influenced 

 their ari'angement. The alteration of a massive feldspathic rock has pro- 

 duced a foliated micaceous or honiblendic one. When tliis alteration of 

 the acid feldspar to the more basic minerals, biotite and hornblende, has been 

 accompanied by the sinuiltaneous sejjaration of ([uartz, the result is a crys- 

 talline gneiss. Phases of strongly foliated rocks are found, from those 

 wliich contain no quartz — that is, a syenite-schist — to those in wliicli (piartz 

 is as abundant as the feldspar, when tlie rock is a gneiss. In t\\v fine 

 grained syenites and schists, in which tlie feldspar occurs in sinall roundish 

 grains, there nuist have been a recrystallization of the feldspar itself if these 

 rocks are transformed massive eruptives, wliicli is l)y no means certain. 



The (piestion as to whether any of the crystalline schists and gneisses 

 of the region are of fragmental origin can not be answered. The roundish, 

 evenly granular appearance of the quartz and feldsj)ar in manv of tliem 

 strongly suggests upon casual examination a clastic origin. However, the 

 more closely they are examined the more clearly it is apparent that this is 

 not sufficient evidence of a fragmental character. It lias been noted that in 

 the gneisses of this class the individuals fit each other perfectlv. The 

 grains as fragmental ones could not possibly have tlms been deposited. 

 If fragmental, either they must ha\e recrystalliz(Ml or else have been enlarged 

 until they interlocked. Eacli of these ])rocesses ami l)oth coiiil)iiu'd are 

 now known to transform fragmental rocks into crystalline ones; but hi 



