626 STRATIGRAPHICAL GEOLOGY. 



This seems to be a more natural association than between sienite and the schists. 

 The discovery of the gneiss here has raised the question whether it may not be 

 the usual floor of the sienite. Sometimes the latter is traversed by planes like those 

 of stratification, but they have not been carefully traced out in this region. The 

 sienite through Exeter is quite broad. Then we have north-westerly dipping schists 

 of the Merrimack group, followed by a narrower band of sienite in the north part of 

 Hampton Falls. At the Baptist church is the gray feldspathic member, perhaps con- 

 tinuous with one of the granitic beds of Rye or Portsmouth. Seabrook shows more 

 variation in the dip, with a bit of sienite and ancient gneiss at the eastern end. 



Fig. io8 illustrates the country between Milton Mills and Alfred, Me., properly con- 

 nected with the previous chapter, and the continuation easterly of Section V. The 

 first rock is the Rockingham mica schist, with south-westerly and westerly dips. A 

 small anticlinal occurs near school-house No. 6 of Acton, where the dip changes back 

 to north-westerly, and the rock is quite ferruginous. Next occurs the andalusite mica 

 schist of the Kearsarge type, not differing greatly from that already passed over. There 

 is a knob of granite on it at its west edge. East of South Acton post-office the dip is 

 10° N. W. About a mile before coming to Mousam pond is a siliceous limestone with 

 gneiss, dipping 5° S. W. This is thought to belong to the Lake series. In the neigh- 

 borhood of Emery's mills in Shapleigh, ferruginous schist of Montalban type dips irreg- 

 ularly 50° S. 80° W. About Spring Vale in Sanford we have similar rocks, with a 

 synclinal axis, the west dips prevailing from the town line. Just in the edge of Alfred 

 the felsite begins ; and at a railroad cut the ledge is distinctly of sienite. The same 

 rock occurs several times before reaching the village of Alfred, the last being at the 

 mouth of Middle Branch. At the village there succeeds a fine-grained granite, a 

 little like that about Merrymeeting lake. 



Fig. 109 shows the relations of the Merrimack schists to the adjacent gneisses. The 

 Salem gneiss has not been observed south of the railroad station, where the dips are 

 south-westerly (p. 561). Inasmuch as south-east dips prevail along the eastern border 

 of the gneiss in Pelham (Section I), they are supposed to continue to the place of this 

 illustration. Near Messer's railroad station the Merrimack schists appear, and are sup- 

 posed to agree with those measured in the north part of Methuen, dipping 20° N. W. 

 These rocks are sandy flags, separated by narrow argillaceous seams. At ledges near 

 Lawrence post-office the strata are vertical. On the northern side of the river are 

 other exposures. In the railroad cut, 150 rods south from the junction in South Law- 

 rence, we find the return of the gneiss. It may not certainly be the same with that in 

 Salem. It contains many rounded spots of feldspar, and several small faults are appar- 

 ent. The dip is thought to be south-east, and within three miles it is reversed ; and 

 there is consequently a synclinal attitude to the strata in the west part of the Andover 

 gneiss. An examination along the strike indicates the presence of a synclinal south of 

 Lawrence in the Merrimack group, so that three axes seem to represent its structure in 

 the figure. 



