104 
AMERICAN GEOLOGY. 
quite flat upon the crest, but quite steep at the base. But in 
the mountains of New England the laminae are steep to the 
summits. Probably diluvial action has swept off those flat¬ 
tened crests which exist in the southern states. 
Fig. ] 9. 
§ 73. Chlorite slate is a green fissile, or slaty rock, with a soft 
feel. In order to make out this rock, it is necessary to recog¬ 
nize chlorite intermixed with quartz, and a structure similar to 
talcose slate. It may contain feldspar and mica. It is often 
associated with gneiss and other schistose rocks. The specific 
gravity of chlorite is 2'72. Its composition is subjoined: 
Silica, 
26-0 
Magnesia, 
8*0 
Oxide of iron, 
43-0 
Alumina, 
18-5 
Water, 
2-0 
Potash, 
2-0 
§ 74. Clay slate. This rock is a hardened clay or shale, and 
is for the most part exceeding fissile. Its colors are green, 
bluish green, and reddish or brown and purple. The red colors 
are variable, from a pink red to a deep brick red. The laminae 
are distinct. 
It is doubtful whether clay slate should be admitted as a 
member of the pyrocrystalline rocks. I should not regard it as 
an eruptive rock, and place it in this connection, were it not 
generally placed among the primary rocks, and were it not 
also quite common in proximity with veins in granite in North 
Carolina and other places. It is, however, possible that this 
