IOWA ACADEMY OF SCIENCES. 
69 
the schistose structure with quartz veins. A little farther 
northwest gneiss appears instead of schist. Here, then, there 
is a passage from slate through schist to gneiss. 
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 Kock 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 gneiss 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 of 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 
