500 STRATIGRAPHICAL GEOLOGV. 



same rocks. On the hill east, about a mile from school-house No. 3, we 

 have a granitic gneiss, and this is succeeded by a pyritiferous concretion- 

 ary schist. South of school-house No. 3 we have the famous Roxbury 

 granite, — a granitic gneiss of the Montalban series. There are also quar- 

 ries along the west base of Horse hill, where the rock is somewhat coarser 

 in texture. On the road south, perhaps three fourths of a mile west of 

 Cummings's pond, we have the concretionary schist. 



In Marlborough this band of rocks becomes wider, and extends east 

 along the north line of the town, taking the place of the concretionary 

 schists of Roxbury, and probably resting on them. Going south-east 

 from Horse hill in Roxbury, after crossing bands of White Mountain 

 and fibrolite schists, we strike another band of concretionary schist, 

 before we reached the line of Dublin, exactly like that in Roxbury; and 

 this band may extend north through Harrisville and connect with the 

 Roxbury schist west of Breed pond. If the schist that we find north- 

 west of West Harrisville is not continuous north-east and connected with 

 a similar rock in Nelson, then we have an oblong area of White Moun- 

 tain and fibrolite schists extending into and partly surrounded by concre- 

 tionary schists. On the south-east side of this area we have fibrolite 

 schists, and they resemble more the schists of Monadnock than the com- 

 mon White Mountain schists. If these are connected with similar schist 

 on the hill north of Harrisville, then we have a band nearly parallel to the 

 Monadnock range, and separated from it by the concretionary schists. 

 In the extreme north-east part of Marlborough, on the line of Harrisville 

 and just south-west of the forks of the stream below West Harrisville, we 

 find the compact fibrolite, so common in the schists of Marlow. This 

 band of rocks outcrops to the south-west near L. Blodgett's, and the east- 

 ern limit here is between Blodgett's and school-house No. 6. From this 

 point the line separating the two schists runs southward near Meeting- 

 house pond, thence near the forks of the road north-west of D. Field's. 

 The boundary here and southward is not so well defined as the southern 

 limit of the band of concretionary rock west of Monadnock is, in the 

 south-east corner of Marlborough, 



The rock of the western and central part of Marlborough is White 

 Mountain schists and gneisses. At the glen above the village there is an 

 extensive exposure of micaceous gneiss. There is a great gorge, with a 



