492 GEOLOGY OF OLD HAMPSHIRE COUI^TY, MASS. 



Approaching the brook the boundary bends northeast, as that on the 

 north side had bent southeast, and down the slope to the brook the diabase 

 is amygdaloidal where nearest the sandstone. The boundaries have 

 approached each otlier so that in the deep side of the narrow brook gorge 

 only a fourth of the width of the great mass appears, but this is well exposed, 

 and a great talus of fragments of a quite coarse diabase makes up the greater 

 portion of its width. The bottom of this narrow gorge is covered with sand. 

 In its opposite east wall one can trace from the south the southward-dipping 

 tuffs, and from the north in fine cliifs the light-buff sandstones with the same 

 dip, to where they approach the eastward continuation of the diabase ; and 

 although the contacts are covered, it can be pretty plainly seen that from 

 both sides the sedimentary rocks abut against the diabase. The latter is very 

 fine-grained and has only a small fraction of the width it had on the other 

 side of the gorge. This gorge is 1 mile northwest of Moody Corners. 



Going east it cuts through the tuff, and where this is coarse and both 

 are decomposed it is very difficult to separate them. In one place the dia- 

 base is quite coarse, light-colored, and greenish from the abundance of 

 diabantite, like that just east of White's wood road, and like the rock of 

 the Deerfield bed at the Deerfeld Notch. Followed still farther east, 

 where it is crossed by the wood road north from Moody Corners, the 

 diabase is on the north dark, fine-grained, and bounded on the north by 

 sandstones which for a long distance east abut against the high Avail of 

 the diabase, as already described. Its botmdary against the tuffs on the 

 south is less clear. Where the road crosses, the distinctly columnar diabase 

 rises in a ridge about 35 feet wide, and yet in this is a mass of tuff nearly a 

 meter across, containing fragments of granite. To the south a narrow 

 swamjj separates it from a rock which seems to be a coarse volcanic agglom- 

 erate made up of angular fragments often 10 to 16 inches across, which in 

 much-weathered exposures can hardly be distinguished from the nonual 

 diabase. 



PETROGRAPHICAL DESCRIPTION. 



1. A section taken from the second outcrop by the roadside going in 

 from Mr. Lyman's house and Batterson's quarry is the typical gray diabase, 

 not distinguishable by the lens from the Iron G-ate rock taken as a type 

 above (page 461), and the microscope reveals little distinction between the 

 two, either in structure or stage of decomposition. Pyrite occurs in excep- 



