IOWA ACADEMY OF SCIENCES. 
67 
of the argillite lies gneiss close to the state line, but mica 
schist a little farther southwest (in Townsend). 
Hitchcock’s geological map of New Hampshire (Rockingham 
Sheet) represents an island of gneiss extending from Mine 
Falls to a mile south of the Massachusetts line near Hollis 
Station (occupy mg a part of the area where Crosby locates 
argillite). This island lies in “Rockingham Mica Schist,” 
extending along the northwest side as an area three and three- 
fourths miles wide, on the average, and along the southeast 
side as an area two and a half miles wide. Both these areas 
of mica schist are represented as continued toward the north- 
east across the Merrimac river and southwest into Massa- 
chusetts. 
It is the object of this paper to mark out and describe the slate 
rock in the vicinity of Nashua (Crosby’s argillite, or the north- 
ern of the two areas marked by Hitchcock as mica schist). 
The Area Briefly Deflned . — The slate rock is found to lie in an 
area six miles wide extending northeast-southwest, just north- 
west of the Nashua river. 
Along the southeast of this area the contact between the 
slate and the adjacent schist and gneiss extends from Runnells’ 
bridge in a northeasterly direction parallel with the general 
course of the Nashua river as far as Nashua, where the river 
leaves the vicinity of the contact. In the city of Nashua the 
contact extends northwestward in a line between Shattuck’s 
ledge and the reservoir. 
Along the northwest of this slate area the boundary- line 
extends from where Gulf brook crosses the slate line, north- 
eastward through the valley just east of Proctor Hill, near 
Long pond, Pennichuck pond and Spaulding’s pond (or Reed’s 
pond, as it is called locally) and crosses the Merrimac river a 
mile below Thornton’s ferry. This line is not perfectly straight 
but curved slightly with the convex side to the northwest. 
Just north of Gulf brook the line curves somewhat suddenly 
toward the southwest, passing between the two exposures half 
a mile northeast of the mouth of Gulf brook. 
Southeast of Nashua no slate was found in the area repre- 
sented on Hitchcock’s map as a branch of this slate there 
marked “Rockingham Mica Schist.” 
General Description of the Slate Area . — The area of slate is 
marked by an extent of lowland occupied partly by swamps 
