250 



slate northwards. The conglomerate is small-pebbled and 

 schistose, containing pinite, with arenaceous beds, which 

 appear to increase and become finer, until the formation is 

 changed to a compact gray slate. All these rocks are greatly 

 disturbed by trap dykes, some of which are quite large, and of 

 coarse texture ; and the slate especially seems to dip in all 

 directions and at all angles ; but the prevailing dip for both 

 the slate and conglomerate is steep — 70° to 80° — to the 

 north. Nearly two miles west of this, on the south side of 

 the railroad, the same conglomerate, with intercalated sand- 

 stone, strikes N. 70° E. with a vertical dip. Near the West 

 Newton Station there is slate just south of the railroad ; and 

 in the vicinity of Auburndale Station, on the same side of the 

 track, conglomerate passing to slate, with a high, nearly verti- 

 cal, north-north-west dip. 



The Conglomerate and Slate in Needham and South JSfa- 

 tich. — Between Auburndale and the crystallines west of the 

 Charles River exposures are wanting ; and towards the south and 

 south-west there is a wide area of unbroken drift. I have repre- 

 sented the conglomerate and slate which we have traced from 

 Brighton nearly to the Charles River as extending south-westerly 

 between the amygdaloid and the crystallines on the north-west, 

 the conglomerate as a double band enclosing the slate, which, as 

 usual, has a synclinal position, the axial plane of the syncline 

 dipping at a variable angle toward the north-west. This nar- 

 row geologic trough is very prolonged, extending through 

 Needham and South Natick nearly, if not quite, to the boundary 

 of Sherborn. The observations upon which these conclusions 

 are based, though few, are fairly satisfactory. 



East of Grantville Station on the Boston and Albany Rail- 

 road, after crossing the petrosilex, there is conglomerate passing 

 to slate, with a north-west dip. According to Mr. Dodge, 

 conglomerate occurs about three-fourths of a mile E.N.E. of 

 Wellesley Station, near the road to Newton Upper Falls. On 

 the road running south from Wellesley, south of Dewing 

 Brook, I found conglomerate with grits, and on the line of the 



