CHAPTER VI. 



GEOLOGY OF THE MERRIMACK DISTRICT SECOND PART. 



InYriHE description of the geology of the Merrimack district is pre- 

 J^ sented in two chapters on account of different authorship. The 

 dividing Hne between the areas described is the western boundary of 

 the largest range of porphyritic gneiss, or that producing the high land 

 between the Connecticut and Merrimack rivers. The geology of the 

 territory west of this boundary has been already presented in Chapter V. 

 The limits of the whole district have been stated in the chapter upon 

 Topography. Speaking geographically, it may be said the area to be 

 described in the present chapter is that of Merrimack and Hillsborough 

 counties entire, with a few towns from Rockingham, Belknap, and Graf- 

 ton. For convenience, the whole of the porphyritic gneiss of Ashland, 

 Meredith, etc., and also the sienite of the Belknap mountains, will be 

 described in the account of the Lake district. Chapter VH. 



The formations occurring in the Merrimack district, as thus limited, are 

 I. Porphyritic gneiss. 2. Lake gneiss. 3. Montalban series, including 

 the Concord granite. 4. Ferruginous schist. 5. Andalusite mica schist, 

 with coarse granitic veins. 6. Rockingham mica schist. 7. Kearsarge 

 andalusite group. 8. Merrimack group, including a little clay slate. 

 There are no eruptive rocks in this area of sufficient importance to find 

 a place upon the map. 



I. Porphyritic Gneiss. 



The largest area of this formation in New Hampshire is that commenc- 

 ing on the north in Groton, expanding at Grafton, narrowing in Wilmot, 



