238 MINERALOGY AND LITHOLOGY. 



In New HamiDshire, the larger part of the rocks called clay slates are 

 on the boundary between clay slate and argillitic mica schist, for the 

 crystalhne ingredients are quite abundant. They possess in a slight 

 degree a micaceous lustre, and in them a variety of minerals are devel- 

 oped. For example : the clay slate from Hanover is all filled with 

 minute crystals of staurohte and garnet, and such rocks are very com- 

 mon in the valley region. These minerals seem to have the capacity of 

 developing under influences that are insufficient to crystallize the other 

 ingredients, but when cut, their sections show them to be extremely 

 impure. The staurolites, under these circumstances, have not assumed 

 their usual twinned forms, but are simple crystals. Some of them are 

 represented in Fig. 4 on PI. 8. 



A clay slate from Pittsburg is all covered with round spots suggestive 

 of garnet. When a section of this slate is examined, these spots are seen 

 to be caused by a deposit of hydrous iron oxide, which probably has re- 

 sulted from the decomposition of minute grains of iron pyrites, which is 

 not uncommon in these rocks. 



The Dixville notch is a good place to note the character of the scenery 

 among slaty rocks, as compared with that of granitic regions. Although 

 there may be exceptions enough, the granitic hills are rounded. In the 

 White Mountain notch, the view, though grand in its immensity, is made 

 by gently curving lines of beauty. The Dixville notch, on the other 

 hand, is rude, jagged, picturesque; for while granite wears with difficulty 

 and loses its corners first, the slaty rocks, when on edge as in the Dix- 

 ville notch, cleave and break down, leaving sharp points and jutting 

 edges. The difference in the character of White Mountain and Alpine 

 scenery is here illustrated. 



QUARTZ SCHIST. 



Quartz schist has already been referred to in the descriptions of the 

 crystalline schists; but some of these rocks bear a resemblance to sand- 

 stones or conglomerates, and though in part composed of crystalline 

 materials, they are also in part composed of angular grains or fragments, 

 and thus they form another connecting link between fragmental and 

 crystalline rocks. The half fragmental character, though often visible in 

 the mass, is much more satisfactorily seen in thin sections ; and in Fig. 



