GEOLOGY OF THE MERRIMACK DISTRICT. 499 



mica schist or micaceous gneiss. It contains the compact fibrolite, and 

 has coarse granitic veins that carry beryl and tourmaline. The strata 

 have a high easterly dip, and there is common gneiss on the west and 

 porphyritic gneiss on the east. 



The band of mica schist in Marlow is less than two miles in width. 

 Its northern limit is near Stone pond, and it is limited on the south-west 

 by the porphyritic gneiss of Bald mountain. Half a mile south of Stone 

 pond the compact fibrolite is very abundant, and is brought out finely by 

 weathering. One of the best exposures is south-west, near S. Mathews's. 



In Alstead the rock changes somewhat, being more compact and more 

 gneissic in its character. In the south-east corner of the town it con- 

 tains coarse granitic veins, where several mica quarries have been worked. 

 The character of the fibrolite also changes, and is more like the common 

 variety. 



South-west, in Surry, we find Surry mountain composed of rock that is 

 more like mica schist than gneiss; though it sometimes has the character 

 of a micaceous gneiss, and sometimes, though rarely, contains fibrolite. 

 On the west side of the mountain, east of the village of Surry, about three 

 fourths of the way up, there is a vein, sometimes two or three feet wide, 

 that carries galena, zinc-blende, and pyrrhotite. It appears also near the 

 north end of the mountain, at nearly the same level. The southern ex- 

 tremity of Surry mountain is the limit of this band of the fibrolite rock 

 southward. The rock of Bald hill, — which seems to be an extension of 

 Surry mountain northward, although cut off from it by the deep valley of 

 the Ashuelot river, — resembles very closely the White mountain gneiss, 

 and probably belongs to the same group of rocks as Surry mountain. 

 We have already referred to the rocks of Bear Den mountain when 

 speaking of the pyritiferous schists, but they are hardly distinguishable 

 from the rocks of Surry mountain, and evidently belong to the Montalban 

 series. 



Then, going south, in the east part of Keene and extending into Rox- 

 bury, and southward in Marlborough and Troy, we find the White Moun- 

 tain schists and gneisses. In Keene, on Beech hill, and on the road east 

 of D. Wood's, we have a micaceous gneiss ;^.also in the hills south-east of 

 South Keene. 



In Roxbury, at school-house No. 3 and on the hills north, we find the 



