5/6 STRATIGRAPHICAL GEOLOGY. 



rock covers the road east of Ash brook in Concord, and west of Jerry hill. 

 Between Jerry and Pine hills the dip is north-west. At the west base of 

 Horse hill, at Mast Yard station, the dip is 55° N. 65° W. By E. C. 

 Elliott's and Mrs. Eastman's the rocks are gneissic, dipping 75° N. 40°W. 

 By E. Terry's is a single lenticular ledge, eight feet long, of the same 

 material. Gneiss with north-west dip appears also by G. Colby's. Per- 

 haps the ferruginous rocks next, in Boscawen, should be included with a 

 later group, but everything in the village of Fisherville properly belongs 

 to this section. The rocks there are ferruginous gneisses, compact dark 

 schists, and fine- and coarse-bedded granites, all dipping north-west. 



5. FiBROLiTE Group with Coarse Granite Veins. 



This band of rock, carrying the best veins suitable for quarrying mica, 

 enters our field of description in Hebron and Plymouth, but I can add 

 nothing beyond what has already been said of them in Chapter V. 



6. Rockingham Mica Schist. 



This term was first used in the report for 1872 (Vol. I, page 55). It is 

 very convenient to designate a large mass of mica schists, with the mica 

 often in coarse blotches and the predominant mineral, by a geographical 

 reference until its proper geological place is known ; and therefore we 

 cannot yet dispense with the term. The closest resemblance is to the 

 micaceous portion of the Montalban series, specimens holding the coarse 

 mica being undistinguishable from many ledges among the White Moun- 

 tains. When large crystals of andalusite occur in the schists it is not 

 easy to distinguish them from the Kearsarge group. There is no diffi- 

 culty in discerning the relations of the formation to the Merrimack group, 

 yet the boundary line between them is not satisfactory. It is thought to 

 correspond with the mica schist division of the Coos group along the 

 Connecticut valley. When well filled with ferric oxide, the rock becomes 

 one of the varieties of the ferruginous division. It is better developed in 

 Strafford than in Rockingham county, but the necessity of separating the 

 group from everything else made itself manifest from the study of the 

 formation in the first named district. 



Two features further characterize the group. First, bands of quartz 

 pass through it, as in some of the older series, before described ; second, 



