68 IOWA ACADEMY OF SCIENCES. 



and ponds* It contains the Nissltisset river, Flint pond, 

 Long pond, Parker's pond, Pennichuck pond, Round pond 

 and Spaulding's pond, besides a large area of swamp. The 

 southeastern part of the slate area is largely occupied by the 

 present valley of the Nashua. 



Within this area the hills of slate rise in ridges to a height 

 of one hundred feel above the adjacent lowland. They do not 

 form continuous ridges, nor does their general direction con- 

 form to the direction of strike. This general direction is N. 

 TO'^ E., while the strike is on the average N. 57° E., though 

 the strike varies a few degrees even in strata but a few feet 

 apart, as the rock is much contorted. These hills are low in 

 contrast with the hills in the gneiss and schist area adjoining. 

 From the top of Long Hill, a hill of the Monadnock type just 

 south of Nashua, these slate hills appear below the Cretaceous 

 peneplain. 



The valleys between these hills, even the hills themselves, 

 are mantled with drift, and the river valleys deeply covered 

 with washed drift; but further reference to this important 

 feature is here omitted as not a part of the problem under 

 consideration. 



Description of the Bocks — The character of the rocks and the 

 relation of them one to another is perhaps best seen along a 

 line from Shattuck's ledge, Nashua, northwestward. At Shat- 

 tuck's ledge, the rock is gneiss in part heavy, in part quite 

 schistose. 



At the reservoir, three quarters of a mile west, occurs slate 

 with bands of graphite. Northwest for three miles the rock is 

 a slate very much crushed and crumpled, and in the northern 

 part of this area, a shaly slate interbedded with gneiss. The 

 dividing lines, then between the slate and the schist, and 

 between the schist and the gneiss, are not definitely marked 

 lines, but are intermediate places in a series of gradations. 



Similar gradations from slate through schist to gneiss are to 

 be found in the southwestern part of the area near the conflu- 

 ence of Gulf brook and Nissitisset river. Here, south of the 

 Massachusetts line, the slate is both shaly and quartzose. 

 Just north of the Massachusetts line quartz veins are very 

 marked in a dark schistose rock. This same structure is found 

 in a railroad cutting near by, revealing in an excellent manner 



*The contour lines of the accompanying map are as given on the New Hampshire 

 state geological atlas. 



