70 



IOWA ACADEMY OF SCIENCES. 



the gneiss east of Mine Falls, where two areas exist: one a mile 

 west of Nashua (Main street) and south of the canal, where out- 

 crops occur at a large quarry, and in the hill just west of the 

 cemetery. The other area omitted is in the northeastern part 

 of the city itself, at Shattuck's ledge, near the Meriimac river, 

 a mile and a half from the outcrops just west of the city. 



It is possible that these two areas should be classed as one, 

 since no outcrops exist between the two areas to tell what the 

 rock between them may be. 



The line boundiag Hitchcock's "Rockingham J\rica Schist" 

 seems to indicate the line between schist and gneiss, as if he did 

 not recognize the slate as a separate rock from the schist. My 

 northwestern line bounding the slate lies about parallel to his 

 line bounding the Rockingham Mica Schist and a mile to the 

 southeast of it. 



Strike. — On the map accompanying this paper numerous dips 

 and strikes may be lound recorded. It now becomes necessary 

 to observe their relation to determine what folds may exist in 

 the area, for there are no strata within the slate area itself 

 whose repetition can indicate the structure. 



Within the slate area and in the gneiss along the northwest- 

 ern boundary the strikes measured are much the same. North 

 of Nashua there is slight evidence that the anticline there tends 

 to form a nose; but all other variations from N. 33° E. are such 



Figure 3. Section northwest-southeast across the area. 



as a badly crushed area might represent; variations too small 

 to be systematized even by minute observations at all points. 

 This general similarity of strike indicates horizontal folds 

 extending in the direction of the strike. 



A study of the dip along lines at right angles to the strike 

 reveals the anticline of a fold running in the direction of the 

 strike along the western half of the slate, while a syncline runs 

 along the eastern half. These are here represented in a dia- 

 gram. (Fig. 3.) 



