GEOLOGY OF MONA DNO CK MO UNTA IN 7 



In this granite are many pegmatite veins, varying from an 

 inch to several feet in thickness, and frequently the pegmatite 

 appears in the schists. Though there is a variation in the direc- 

 tion of these veins, the prevailing one is northerly in the southern 

 granite lobes. This pegmatite material shows all grades of 

 variation from the well-defined, coarse pegmatite to pure vein 

 quartz; and all the variations evidently had a common origin.^ 



From what has been written, it is evident that schist and 

 granite were modified by mutual contact. The extensive seri- 

 citization of one and the darkening of the other by the increase 

 of biotite are the most noticeable effects. From these contact 

 phenomena and from the schist inclusions in the granite it is 

 evident that the granite is intrusive and younger than the schist. 



In rocks so thoroughly recrystallized as are the schists of our 

 study no fossils can be expected, but the graphite found in both 

 the rusty graphitic schist and also, though rarely, in the fibrolitic 

 schist may point back to organic remains.^ To one acquainted 

 with the rocks in the plateau of central Massachusetts, from 

 Worcester to the Connecticut Valley, it is evident that these 

 schists in and around Monadnock are but a continuation of the 

 Massachusetts rocks, though there may be a few square miles of 

 area between the two not yet mapped ; and the conclusions that 

 have been reached from the study of the latter are applicable to 

 the former. After many years of study. Professor Emerson and 

 the writer have concluded that the schists of this plateau in 

 Massachusetts are more highly metamorphosed phases of the 

 Carboniferous phyllite and quartzite found at Worcester.3 If 

 this conclusion is correct, then these schists of Monadnock are 

 Carboniferous, and the intruded granite is post-Carboniferous. 



Another fact demanding careful study is the attitude of the 

 schist in this mountain. That the structure is not as simple as 

 it might be is indicated by the statement on p. 639, Vol. II, of 



'J. E. Spurr, "Genesis of Auriferous Quartz Veins," Eighteetith Anmtal Report 

 of the U. S. Geological Survey, Part III, pp. 311, 313. 



^In the Geology of New Hampshire, Vol. II, p. 503, a graphite mine in this schist 

 is mentioned. 



^Geology of Worcester, Massachusetts, pp. 28, 50, 137, 139, 148, 152. 



