STRUCTURAL GEOLOGY OF HANOVER DISTRICT, NEW HAMPSHIRE 673 



While previous work 2 on this district showed that this 

 igneous rock was younger than the overlying sediments, 

 it did not show its relation to the metamorphism of those 

 sediments, the structure, or the interrelation of the central 

 core of granite to the border-zone phase. 



The structure (figure 2) is that of an eroded dome, with 

 granite at the center. There are two phases of this gran- 

 ite : (1) a central mass, 9&, which is pink or very light 

 gray, not deeply weathered, and shows practically no 

 foliation; and (2) surrounding this, a border zone of 

 granite gneiss, 9a, showing considerable foliation in places, 

 and differing in composition in the absence of muscovite 

 and the presence of a much larger content of basic min- 

 eral. This is cut in places by dikes of the younger gran- 

 ite and was rendered schistose either before or during this 

 intrusion. Overlying the granite-gneiss border zone are 

 the following, in ascending order: sandy schist with 

 squeezed quartzite pebbles, 3; slate and mica schist, 4, 

 and quartzite conglomerate, 5. All of these have been 

 intensely foliated and variously affected by contact meta- 

 morphism. The argillaceous rocks are altered most. The 

 alteration is so great in places that the metamorphic rocks 

 are distinguished from igneous rocks with difficulty. The 

 new minerals formed are hornblende, garnet, and chlori- 

 toid, the hornbl^de in places composing more than half 

 of the rock. O^^m the quartzite is rendered micaceous, 

 a white quartz itejpscoming speckled and resembling light 

 gray granite. Sometimes the quartzite conglomerate, es- 

 pecially where some argillaceous material occurs within 

 it, is highly altered and difficult to recognize. In all cases, 

 however, the original sedimentary character of these rocks 

 may be recognized in thin sections, and in most cases in 

 the hand specimen when closely studied. Occasional trap 

 dikes cut the granite and the sediments near their contact 

 with the granite. 



On either side of this dome is a synclinal fold, the one 

 on the west, however, showing younger sediments, which 

 have been removed from the syncline to the east (figures 

 1 aud 2). 



Professor Hitchcock 3 describes certain "inclusions" as 

 "fragments of the adjacent mica schist." It is to be 

 noted, however, that these "inclusions" are found all the 

 way from the outside edge of the border zone to the cen- 

 ter of the Lebanon granite, a distance of no less than a 

 mile from the border. It is difficult to conceive how 

 fragments, most of them less than two inches in diameter, 

 could be carried to that distance from the contact and 



to 



g< 



bOQ 



2 C. H. Hitchcock : Geology of the Hanover, New Hampshire, quadrangle. Sixth Re- 

 port of the State Geologist of Vermont, 1908, pp. 139-186. 

 "Op. cit., p. 165. 



