6l2 STRATIGRAPHICAL GEOLOGY. 



gneiss. 2. Lake gneiss (including the Laurentian of Massachusetts) 

 3. Montalban. 4. Rockingham group. 5. Merrimack group. 6. Kearsarge 

 group. 7. Huronian and Cambrian of Massachusetts. The unstratiiied 

 rocks are the sienites of Exeter and Pawtuckaway, inferior granites, and 

 the well-developed granites and porphyries of York county, besides a 

 great many trap dykes along the coast. 



I. PoRPHYRiTic Gneiss. 



Only a relic of this ancient formation appears in this district, and that 

 is at the extreme south-eastern corner, in Seabrook. It lies at the north- 

 east end of the sienitic range. The crystals are small ; and the rock is 

 traversed by segregated veins. Perhaps it had better be ranked with 

 the eruptive mass of Green mountain, or with the Lake gneiss. Its 

 association with the sienite reminds one of the like condition of things 

 to be described presently in Brentwood. The ledges appear in the salt 

 marsh region near the mouth of Little river, and are frequently covered 

 by the tide. 



2. Lake Gneiss. 



Five principal areas of this formation may be mentioned in this field : 

 (i) in the corners of Barnstead, Alton, New Durham, and Farmington; 

 (2) Strafford and Northwood ; (3) Barrington to Candia, connecting with 

 the Deerfield-Mason range; (4) the Hampstead range, with the small 

 patches in Chester, Epping, and Fremont ; (5) the north end of an 

 ancient range from Massachusetts, terminating in North Andover and 

 Boxford. 



The Barnstead and Northwood Areas. These are isolated patches, 

 almost on the same line of outcrop, each about eight miles long. The 

 first is mainly restricted to the elevation known as New Durham ridge, 

 there being a small village upon the summit. At school-house No. 3 the 

 gneiss dips 5° N. W. By the Free-will Baptist church, at the very high- 

 est point, the layers are exceedingly twisted, with micaceous and ferrugi- 

 nous seams, dipping 20° S. E. Coarse granite veins twenty-one feet wide 

 cut the strata. At L. S. Nute's, in Alton, the dip is S. 30° W. For a 

 mile or more the north-west strike predominates. At J. Morrison's the 

 dip is south-east. Drift covers the ledges on the north side of Half- 



