40 STRATIGRAPHICAL GEOLOGY. 



it that these metamorphic rocks seemed to be only altered strata. But 

 we have in New Hampshire and Maine fossiliferous rocks of Lower Hel- 

 derberg, resting on or associated with rocks which he referred to the 

 metamorphic Quebec group. 



We now give in detail the lithological characteristics of the rocks of 

 the Coos group, and its geographical limits in northern New Hampshire. 



If we draw a line from a point on the boundary, two and a half miles 

 east of Third lake, and have it run nearly parallel with Perry stream, con- 

 tinuing it south, it will cross the east end of Back lake, will pass half a 

 mile west of D. Blanchard's, and cross the road running along the Con- 

 necticut near the house formerly owned by T. Blanchard. Extending it 

 south through Clarksville, it will cross the Dead Water stream a mile east 

 of the terminus of the road that runs east through the town, then, bend- 

 ing a little to the east, it passes half a mile east of Alden Fletcher's in 

 Stewartstown, thence southward to J. Young's, near Bear rock, thence 

 directly south across Colebrook and Columbia, almost to Sims stream, 

 then, turning nearly at a right angle, it extends to the Connecticut. We 

 have the eastern boundary of the Coos group in the towns through which 

 the line is run. An extension of the line northward into Quebec province 

 would cross the north end of Lake Megantic. Near the mouth of Sims 

 stream it seems to have been crowded out by the sienite. Before follow- 

 ing the line where this group comes up south of the sienite, we shall 

 describe the rocks included in the northern section. They consist for 

 the most part of argillaceous schists. In places, and perhaps more com- 

 monly near the eastern border, the strata are so wrinkled and corrugated 

 that it is often difficult to determine the dip. In many places, interstrati- 

 fied with the wrinkled masses, are strata in which the laminae are thicker, 

 and, when separated, present a smooth surface. This has almost invaria- 

 bly small cavities disseminated through it, which are filled with a brown 

 powder, resulting, probably, from the decomposition of a lime mineral, 

 containing protoxide of iron : the lime being removed, the iron would be 

 converted into a peroxide, whence the brown color. This brown powder 

 is so abundant that it sometimes gives a coloring to the whole rock. 

 While more abundant in the rocks that have a regular cleavage, yet 

 sometimes the cavities are scattered through the wrinkled varieties. In 

 some cases the schist that has an even cleavage contains an abundance 



