346 Pirsson and Washington — Geology of New Hampshire. 



of different composition in small amounts which now appear as 

 accompanying intrusive masses and dikes. Since then the 

 superincumbent rocks have been removed by long-continued 

 erosion, which has also bitten deeply into the igneous mass as 

 well, but this has resisted better than those which surround 

 it, and in consequence the igneous stock now projects as a 

 rough mountain tract. Lastly, much material was removed at 

 the time of the glacial invasion and the rock surfaces left 

 scored and polished. 



The enclosing rocks. — These are mostly gneisses and mica 

 schists, rocks of metamorphic character. Although they do 

 not especially concern us in this paper, a word or two may be 

 added regarding them. On the eastern side the contact is with 

 a heavy solid gneiss, composed of quartz, alkali feldspars and 

 biotite, and often carrying reel garnets. In its texture it is 

 rather irregular, not presenting that evenness of aspect fre- 

 quently shown by gneissoid granites, and it is possible that 

 detailed study in the future may show that it is of sedimentary 

 origin. It has a wide extension in this general region and has 

 been called the AVmnepesaukee gneiss by the Hitchcock Survey. 



In Mount Major and Pine Mountain are two small masses 

 of a porphyritic granite as shown on the map of the Hitch- 

 cock survey. • In their report it is spoken of as the porphyritic 

 gneiss. It covers a large area to the north of this region, where 

 we have seen and studied it to some extent. By its general 

 characters, contact modifications, etc., it is . clearly an igneous 

 rock — a granite which carries large, often huge, phenocrysts 

 of orthoclase. It occurs in other parts of New England and 

 is a type worthy of especial study. It sometimes has a pro- 

 nounced gneissoid structure which evidently is often a fluxion 

 texture, at other times it is due to dynamic shearing and in 

 some places it is quite devoid of any gneissic character. 



On the west and south the Belknap massif is in contact with 

 micaceous gneisses, micaceous slates colored dark with organic 

 matter and iron ore and with mica schist rocks evidently of 

 sedimentary origin. The boundaries and names of these forma- 

 tions are those given on the Hitchcock map. The lack of 

 printed symbols on this map connecting the legend with the 

 outlined areas and the great similarity of colors makes it 

 exceedingly difficult, in many cases impossible, to determine 

 what some of these areas are meant to be, nor does the text 

 afford much help in this direction. The formations are men- 

 tioned in many places, but there is no definite description of 

 them given in a systematic manner by which their characters 

 may be recognized. From what is stated,* however, we con- 

 clude that the rocks on the west belong to the Montalban series 



* Op. cit., vol. ii, p. 600. 



