LITHOLOGY. 239 



5 on PL 12, a section of such a quartz schist is represented. Several 

 large fragments of quartz and one of plagioclase are seen, but they are 

 all surrounded by a perfectly compact mass of quartz, which without 

 polarized light shows no granular structure, or any divisional lines 

 which might indicate the cementation of grains, and between crossed 

 Nicols it appears as usual like a complex aggregate. The large quartz 

 grains have been somewhat affected, for their edges are sometimes 

 indistinctly blended with the mass ; and their interior structure often 

 appears complex in polarized light, as if, by the influences which must 

 have acted upon them, they had been altered from homogeneous grains 

 into aggregates of granules. The mass of the rock around these grains 

 is clearer than elsewhere, and the impurities that are contained in the 

 rock bend about these fragments in something of the way that the little 

 crystals in basalts are arranged around the large ones. 



With these half fragmental rocks our studies come to an end, for the 

 characteristic rocks of New Hampshire are crystalline. In this connec- 

 tion, the great granite breccias at the Notch and at Franconia should be 

 called to mind as most wonderful examples of half fragmental rocks, in 

 which, however, the fragments are so immense that they and the ground 

 mass in which they are imbedded have both been considered under gran- 

 ite. The slates of Mt. Pequawket, which are all cemented together by a 

 paste of quartz porphyry, should also be recalled; but this rock, also, has 

 been made by such an exceptional method, that it is much more instruc- 

 tive to consider it among the quartz porphyries. 



FRAGMENTAL ROCKS. 



Our consolidated rocks being therefore exclusively crystalline, it will 

 be profitable to consider, for comparison, a really fragmental rock. The 

 . Connecticut red sandstone extends up the valley from the Sound, and 

 reaches the border of our state, and should receive some attention. This 

 rock is often quite hard and compact; and I have filled the last space on 

 the last plate with a representation of a thin section of the finest variety 

 of the celebrated and beautiful Portland building stone as it appears in 

 polarized light. It will be noted, then, how marked is the contrast be- 

 tween a truly fragmental rock and all the rocks which have been consid- 



