IOWA ACADEMY OF SCIENCES. 69 



the schistose structure with quartz veins. A little farther 

 northwest gneiss appears instead of schist. Here, thee, there 

 is a passage from slate through schist to gceiss. 



Just west of Hollis Center is still another opportunity to 

 observe an approach to the dividing line between the slate and 

 the schist, though not so good as either of the two already- 

 described. Just west of Hollis Center there is slate. This 

 grades through schist to the gneiss quarried at Proctor Hill. 



Southeast of the slate area are several outcrops of gneiss: 

 one at Shattuck's ledge in the northeastern part of the city of 

 Nashua, another in the western part of the city, where it is 

 quarried in one place, a third on the Nashua river, five miles 

 above Nashua, a fourth at Flat Rock quarry, and again at Long 

 Hill, south of the city. 



The sudden transition from slate to gneiss close to the 

 Nashua river will be referred to under the heading "Faults." 



Eastward from Runnells' bridge, near Hollis, there is a gra- 

 dation from the slate through schist to the gneiss at Flat Rock 

 quarry, and a similar gradation from schist to eneiss between 

 Nashua and Long Hill. 



Thus southeast there is a gradation from slate through schist, 

 schist with quartz seams to gneiss, similar to that from the 

 slate area northwest. 



Attempts to Harmonize Descriptions of Crosby and Hitchcock. — 

 The above description of gradations in the character cf the 

 slate, schist and gneiss, suggests an explanation of an apparent 

 lack of harmony between Crosby and Hitchcock. Crosby dis- 

 tinctly records gradation between the three rocks, and because 

 of this gradation seems to call both the slate and the schist 

 argillite, even though the argillite southeast of Nashua is 

 exceedingly clear mica schist. Judging by the map, Hitchcock 

 apparently recognizes the same gradation between the rocks, 

 though I find no description in the text to confirm this infer- 

 ence, and calls both schist. I fear, however, that because of the 

 schistose character of many of the slate outcrops, the area of 

 slate has been entirely neglected. 



Concerning Hitchcock's location of the gneiss area along the 

 Nashua river, between Mine Falls and just south of the state 

 line, there is a single area of probable gneiss on the river about 

 four miles west of Nashua. This area is cut off on the south- 

 west by slate just south of Runnells' bridge, and on the north- 

 east by mica schist at Mine Falls. Hitchcock has overlooked 



