GEOLOGY OF THE MERRIMACK DISTRICT. 549 



break in the quartz. 6. The mica schist seems to have been deposited 

 after the first period of elevation affecting the Lake gneiss. Hence the 

 mountains of it in the Pack Monadnock and Lyndeborough ranges may 

 not have exerted a marked influence in producing the break. It could 

 easily conceal quartz bands by covering them up. 7. An anticlinal ridge 

 composed of quartz would withstand denudation much longer than the 

 enclosing rock alone. Hence certain comparatively isolated ridges of 

 this quartz may represent the tops of underlying formations. Such are 

 the supposed continuation of these quartz bands in Strafford, Wakefield, 

 Effingham, far beyond the limits of the Merrimack district. 8. Quartz 

 bands similar to these occur in the Montalban and Bethlehem gneiss ; 

 also in the Lisbon, Merrimack, and Rockingham groups. They occur on 

 both sides of the central ridge of the state, usually much more isolated 

 than the cases recently considered. Care must be exercised not to con- 

 found together these bands that were deposited in different ages. 9. The 

 occurrence of fragments of quartz in the drift throughout the state 

 furnishes admirable illustrations of the dispersion of boulders by the ice. 

 Many localities have been discovered through their instrumentality, and 

 we have evidence to suggest the existence of these ledges in localities 

 now obscured by surface accumulations. 



Additional Fads. There remain to be stated a few further facts and 

 observations respecting the gneisses between and to the north of these 

 quartz ranges. In Hooksett, three types of rock approach one another, 

 and I do not feel satisfied that their respective limits have been properly 

 assigned. The distinctions were not drawn till after the comjoletion of 

 field work, and therefore perplexing questions arise respecting the proper 

 hmits of each. The ferruginous and Rockingham schists contain large 

 granite beds, which often closely resemble the Concord granite. When 

 the adjacent schists are intermediate in texture between the Rockingham 

 and Montalban, it becomes difficult to decide with which formation a 

 particular granite should be placed. There is also a close resemblance 

 between the Concord granite and some of the Lake gneisses, as, for 

 instance, those of Salem. The radical distinctions between all these 

 groups are well founded, and if opportunity were afforded for further 

 examination of their distribution, I do not doubt that entire satisfaction 

 respecting their territorial limits would be attained. As it is, I will draw 



