GEOLOGY OF THE MERRIMACK DISTRICT. 577 



beds of granite are innumerable. They are often of sufficient conse- 

 quence to be specially colored upon the map. These two features show 

 how closely the formation imitates the Montalban. As regards elevation, 

 the strata are commonly inclined at small angles, with numerous local 

 foldings, and they constitute mountain masses when slightly inclined. 

 These characteristics agree with their reference to a comparatively mod- 

 ern period for their deposition. The grinding up of the Montalban strata 

 would furnish the materials for the recomposition of ledges very similar 

 to them, and at their junction the differences might be so slight as to pre- 

 vent a ready recognition of the discordances in stratigraphical structure. 

 It has been stated heretofore that this group is spread like a blanket 

 unconformably over several of the older gneissic groups. This statement 

 still seems to be correct. In our delineation of it in map No. 5 of the 

 physical history of the state, the color is made to embrace on the north- 

 west side the Kearsarge group and the fibrolite rock with coarse granite, 

 and on the south-east the Merrimack groups. A small area near Umba- 

 gog lake is also placed with it, which is reckoned as Huronian on the 

 final map. 



In the Merrimack district the following areas of this rock will be noted : 

 (i) in Sanbornton ; (2) (3) branches of the enormous Strafford county 

 blanket, prominently occupying Canterbury and Northfield on the north, 

 and Allenstown and Epsom on the south ; (4) (5) at least two long 

 narrow bands between the quartzes of Hillsborough county ; (6) the 

 Lyndeborough and Temple mountain range ; (7) Mt. William in Weare ; 

 (8) that associated with the Merrimack group, between the Manchester 

 and Hampstead gneissic areas. 



Sanbornton. This area touches the porphyritic gneiss and the Great 

 bay on the north-east, small patches of Lake gneiss on the north and 

 south, and Montalban on the south-west. It does not seem to cross 

 either the Winnipiseogee or Pemigewasset rivers, though reaching to the 

 banks of both streams. On the slope towards Great bay, the ledges are 

 mostly concealed by a sloping mass of drift. The granite of the series 

 appears north of O. Calef's. Going north from Tilton the boundary of 

 this group is reached at the "gulf," the dip changing abruptly to the 

 south-east instead of north-west. It changes back again a mile north of 

 the "Square," near W. Paine's, 60° N. 27° W., also 30° N. 60° W. The 

 VOL. II. 73 



