CLASSIFICATION OF THE NEW HAMPSHIRE FORMATIONS. ^^J 



The Labrador system, if present in New Hampshire, is in very limited 

 amount. Recent investigations make it difficult to say that the labrador- 

 ite rocks are not of eruptive character. They have the composition of 

 dolerite; and certain exposures of them upon Mt. Washington are surely 

 injected dykes. Hence great doubt arises whether the larger area of 

 Waterville really represents the Labrador system of Canada. At all 

 events, its age is great, for these dykes cut through Montalban strata. 

 This dolerite may be regarded as one of the oldest eruptive rocks in the 

 state, coming to the surface in what was the Labrador age of the world. 



Next there is an enormous surface occupied by various types of mica 

 schist. They much resemble one another, and are confined to the region 

 south of Winnipiseogee lake, unless one or more of them should be made 

 the equivalent of the Coos group along Connecticut river. We have the 

 local names of Rockingham, Kearsarge, and Merrimack applied to them. 

 Of these the second is characterized by the abundant presence of andalu- 

 site ; and the formation lies unconformably upon the Montalban at Mts. 

 Monadnock and Kearsarge. In the sections across the mica schist group 

 at Derry (Fig. lOo) its synclinal structure is very obvious, resting upon 

 the Lake group. The Merrimack group holds a similar relation to the 

 gneisses, as in the Massachusetts section (Fig. 98) and between North 

 Andover and Salem (Fig. 109). The Merrimack rocks would seem to 

 rest upon the Rockingham, and probably the Kearsarge series does the 

 same. 



The eruptive rocks are not readily assigned to comparative ages, since 

 the epoch of eruption cannot usually be fixed closely. There are three 

 general centres of their distribution within the limits of our map. The 

 largest is in the midst of the White Mountains ; the next occupies the 

 northern part of the same mountain group, divided midway by the Grand 

 Trunk Railway ; the third is in Essex county, Vt. Perhaps the labrador- 

 ite diorites, and some of the dolerites cutting the older gneisses, should 

 be ranked as the first rocks that have been injected. The principal erup- 

 tive masses seem to have made their appearance in the debatable period, 

 either at the close of the Eozoic or early in the Paleozoic. They are the 

 Conway, Albany, and Chocorua granites, sienites, and other granites. 

 The porphyry has preceded these granites, since fragments of the former 

 occur in the latter rocks. There are dolerites mineralogically like those 



