GEOLOGY OF Till'. COAST DISTRICT. 6\ $ 



projection of all Iho fucL.s at comiiiaiul ccrlainly siip^f^csts tlic direct con- 

 nection of the ICpping and Fremont gneisses with the JIampslead area. 

 In Brentwood a few ledges of this gneiss, dipping 70" S. 60" W., with 

 joints inclined S. 40'' K., appear to the east of a Congregational (iiiirch, 

 more than a mile west of Marshall's corner. It adjoins sienile, and does 

 not extend far along the line of strike. 



Massac// r/.u-t/s Area. The map i)resents to view seven or eight miles' 

 length of the north-cast end of a very important gneiss band, called 

 Laurentian by some, and designated as Atlantic upon i'late I. It is 

 noted upon page 23 as forming the outermost of the formations encir- 

 cling the Boston basin concentrically. 'Die section (I'late 11) gives it a 

 monoclinal north-west dip. Concerning this gneiss in Andover and 

 North Andover, I wrote the following in i<S67,* including a notice of a 

 very coarse granite : 



The gneiss foimalion includes ;in ii;;ly I<)()kin<i; gneiss,— a very (cniii^inous variety, — 

 quartzites in limited amount, nnicli rinc-j^Maincd j^rauitc^ a bed ui slcalilc, and jicrliaps 

 Other varictie.s worthy of notice. It occupies most of the area of tiie two towns, lyin;^ 

 north-west of the hornblende rock, and limited by an overlyinj^ mica schist on the Mer- 

 rimack river. South of Aslcbc hill is a fine-grained granite, uui. far Irom the steatite 

 bed atW. Jenkins's .saw-mill. 'I'lic first ledge oljservcd wcstof Asiebe hill is (|iiarl/,ile. 

 Patches of the fine-grained granite were noted at J. Cummings's, near Carmel hill ; in 

 small amount at the railroad 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 almshouse, and in many other places. There may be a .synclinal 

 structure in this formation, for at the South Andover station the dip is 80° N. 67^ W., 

 and 46° S. E. west of West Andover church. In several other places east of Shaw- 

 sheen river the north-westerly dip was noticed ; and it is my impression that the south- 

 easterly dip prevails in the railroad cut at South Lawrence. Along the north-western 

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

 ance of small pebbles. I am uncertain whether it belongs to the gneiss below, or to 

 the mica schist above. 



The coarse granite apjjears on the map like a flattened ellipse, with sharp ends cut- 

 ting the gneiss at an angle of about twenty-five degrees. 1 have not searched for it 

 south of Foster's pond ; but to the north from that point, as far as IJ. Rogers's in the 

 north-east corner of the Phillips district, the outcroi)s are very numerous. From the 

 middle of Scotland district to a point west of Moses Abbott's, nearly a mile and a half, 



* Proc. Essex Institute, vol. v, p. 157. 



