LITHOLOGY. 239 
s 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- 
