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varieties of rock in Andover : 1. Hornblende schist, including syenitic 

 masses apparently intruded after the formation and perhaps meta- 

 morphism of the schist; 2. Gneiss, with similar patches of fine- 

 grained granite ; 3. Very coarse granite ; 4. Fine mica schist. 



The first group is found in the south-east part only of the towns, 

 or south of a line drawn from near J. Farnham's in the Farnham 

 School District to the four corners at the base of Aslebe Hill, thence 

 probably curving below W. Jenkins' saw-mill and running to S. Cheev- 

 er's in the Scotland District, thence to about" the corner at the meet- 

 ing of the towns of Andover, Wilmington, and Eeading. Very much 

 of this formation is properly a gneiss, with hornblende in the place of 

 mica. Commonly the divisional planes of stratification and of joints 

 are very even. One of the largest- masses of syenite observed occu- 

 pies Aslebe Hill and the territorj^ to the east on the road to Middleton. 

 A mile west of Gray's saw-mill the strata dip 60° N. W. 



The gneiss formation includes an ugly-looking gneiss, a very fer- 

 ruginous variety, quartzites in limited amount, much fine-grained 

 granite, a bed of steatite, and perhaps other varieties worthy of notice. 

 It occupies most of the area of the two towns, lying north-west of the 

 hornblende rock, and limited by an overlaying mica schist on the Mer- 

 rimac River. South of Aslebe Hill is a fine-grained granite, not far 

 from the steatite bed at W. Jenkins' saw-mill. The first ledge ob- 

 served Avest of Aslebe Hill is quartzite. Patches of the fine-gi'ained 

 granite were noted at J. Cummings's, near Carmel Hill ; in small 

 amount at the I'ailroad station at South Andover ; near J. Adams's on 

 the south shore of North Andover Pond; several localities south- 

 west from the "West Andover Cemetery ; at about three-fourths of a 

 mile north from "West Andover church at J. Chandler's, near the Alms- 

 house, and in many other places. There may be a synclinal structure 

 in this formation, for at the South Andover station the dip is 80° "W. 

 23° N., and 46° S. E. west of West Andover church. In several other 

 places east of Shawsheen River the north-westerlj^ dip was noticed, 

 and it is my impression that the south-easterly dip prevails in the 

 railroad cut in South Lawrence. Along the north-west boundary of 

 this group there is a belt of peculiar gneiss, whose feldspar has the 

 appearance of small pebbles. I am uncertain whether it belongs to 

 the gneiss below or the mica schist above. 



The coarse granite appears on the map like a flattened ellipse with 

 sharp ends cutting the gneiss at an angle of about 25°. I have not 

 searched for it south of Foster's Pond, but to the north from that 

 point, as far as B. Rogers' in the north-east corner of the Phillips Dis- 

 trict, the outcrops are very numerous. From the middle of Scotland 

 District to a point west of Mos3S Abbott's, nearly a mile and a half, 



