138 AZOIC AGE. 



common to color the regions covered by crystalline rocks all alike, 

 without reference to their differences of age. Thus the metamor- 

 phic rocks of various ages are confounded, as they are also in the 

 unfortunate name they sometimes bear, of hypogene rocks. 



Kinds of rocks. — The rocks are mostly of the metamorphic 

 series, related to granite, gneiss, syenite, and the like. But they 

 embrace only the most ancient of these rocks ; for the granites 

 and schists of New England, of Cornwall, the Alps, and many 

 other regions, belong to later ages.. 



Besides true granite and gneiss, there are diorite, — a rock consisting 

 of feldspar (albite) and hornblende without quartz (§ 84) ; also 

 extensive ranges of coarse granite-like rocks of grayish and 

 reddish-brown colors, composed mainly of crystallized labradorite 

 or a related feldspar (§ 55), or of this feldspar with the addition 

 of the brownish-black and bronzy foliated mineral hypersthene 

 ($65), and constituting the rock called hyperite ; also chlorite schist, 

 while mica schist appears to be absent ; also serpentine, limestone 

 (or statuary marble), granular quartz (a hard sandstone), and in 

 some places a hard conglomerate; also magnetic and specular iron-ore in 

 immense beds. 



There are, in addition, porphyry of green, brown, and reddish colors; a 

 garnet-euphotide (eelogite) and a feldspar-euphotide ($85); soapstone (Rens- 

 selaerite) (§ 86, [4]); parophite rock and schist ($£ 67, 87); pyroxene rocks ; 

 ophiolites or verd-antique marble of different varieties (£ 86, [8]). 



Part of the feldspar related to labradorite has the composition of andesine 

 or vosgite ; and oligoclase exists in the Swedish Azoic. The Labrador rock 

 turns gray on weathering. Part of the hyperite contains ordinary hornblende 

 instead of hypersthene, and some kinds mica or epidote. The hypersthene is in 

 foliated pieces or crystals often a little bronze-like in lustre. Good localities for 

 the opalescent labradorite are the streams of the Adirondack, — especially, says 

 Professor Emmons, the beaches of East River ; also Avalanche Lake, near the 

 foot of the great slide from Mount McMartin. 



The potstone or soapstone called Rensselaerite covers considerable areas in 

 the towns of Fowler, Canton, Edwards, Hermon, etc., St. Lawrence co., and 

 at Grenville, in Canada, and is cut into slabs for tables, chimney-pieces, fur- 

 nace-linings, or made into inkstands. The parophite or aluminous potstone 

 of Diana, Lewis co., N.Y. (§ 87), is also used for inkstands, etc. 



Beautiful red and green porphyry and a buhrstone are found at Grenville, 

 Canada. 



As crystalline rocks have been formed in various ages, — those 

 of New England, for example, long after those of the Azoic, — it is 

 possible that some Azoic rocks have undergone a second or third 

 alteration subsequent to the original one in the Azoic age. It may 

 be difficult, in fact, to say which of the rocks retain their original 



