IOWA ACADEMY OP 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 (occupyicg 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 Defl^ned. — Tte 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 



