6^6 STRATIGRAPHICAL GEOLOGY. 



Section I. 



The first section follows the most southern tier of towns in the state, 

 and is made to extend to the Atlantic ocean, in the south part of Ipswich 

 in Massachusetts. Our collection of specimens commenced at Lawrence. 

 The section delineated is about ninety-six miles in length, ten miles dis- 

 tance being in Vermont, beyond Connecticut river. 



At the east end next the ocean is a broad stretch of salt marsh. There 

 is a broad band of sienite next, followed by hornblende schist. In George- 

 town is the hornblende schist range, possibly of Huronian age. Boxford 

 and North Andover exhibit the gneiss, called Laurentian by some, and 

 much like the Lake group of New Hampshire. After this, in the Merri- 

 mack valley through Lawrence, Methuen, and Dracut, we find the Mer- 

 rimack group dipping usually at a high angle to the north-west. The 

 gneiss east of Lawrence dips easterly; and there may follow, first, a syn- 

 clinal before reaching Essex street, Lawrence, then an anticlinal, the west 

 end having a smaller dip {see Fig. 109). The junction of this Merrimack 

 quartzite with the Pelham gneiss is not seen ; but the dips in Dracut and 

 Pelham indicate that the pressure has been exerted so as to fold the anti- 

 clinal beneath the westerly-dipping gneiss at N. Hobbs's. The gneisses 

 in the extreme east and west parts of Pelham dip towards each other, 

 though the presence of a porphyritic gneiss at J. Gage's, west of the vil- 

 lage, suggests a double synclinal resting upon an older rock between. 

 There are materials for two axes in Hudson, the western border of the 

 gneiss dipping 50° N. 30° W. at a turning-shop. 



Next there is the broad valley of mica schist of the Nashua valley, 

 referred to the Rockingham series, and making a double basin with a 

 narrow range of gneiss in the middle. This extends into the edge of 

 Brookline. Proctor hill furnishes examples in the western part of the 

 micaceous area of the interesting feldspathic or granitic beds, such as 

 have been noticed farther to the north-east. A range of Merrimack slate 

 seems to belong to the middle of the band, in the west part of Nashua. 

 The Lake gneiss following displays a prominent anticlinal along the west 

 line of Brookline, with a probable synclinal to the cast of the village. In 

 Mason there is so much divergence between the dips east and west of 

 the railroad as to suggest the presence of a folded westerly inclined anti- 



