70 



LITHOLOGICAL GEOLOGY. 





9. Stalagmite, Stalactite. — Depositions from waters trickling through the roofs 

 of limestone caverns form calcareous cones and cylinders pendent from the roofs, which 

 are called stalactites, and incrustations on the floors, which are called stalagmite. The 

 waters, filtering down from the overlying soil, contain a little carbonic acid, and are 

 thus enabled to dissolve the limestone, which is deposited again on evaporation. The 

 layers of successive deposition are usually distinct, giving the material a banded ap- 

 pearance. 



2. Crystalline Limestone. 



1. Granular Limestone (Statuary Marble). — Limestone having a crystalline gran- 

 ular texture, white to gray color, often clouded with other colors from impurities. 

 It is a metamorphic rock; it was originally common limestone; it became crystalline 

 under the action of more or less heat ; in the process, all the fossils present were 

 obliterated, except in some cases of partial metamorphism. Its impurities are often 

 mica or talc, tremolite, white or gray pyroxene or scapolite ; sometimes serpentine, through 

 combination with which it passes into ophiolyte (p. 75); occasionally chondrodite, apa- 

 tite, corundum. 



Varieties. — a. Statuary Marble; pure white and finegrained, b. Ornamental 

 and Architectural Marble ; coarse or fine, white, and mottled of various colors, and, 

 when good, free not only from iron in the form of pyrite, but also from iron or man- 

 ganese in the state of carbonate with the calcium, and also from all accessory minerals, 

 even those not liable to alteration, and esDecially those of greater hardness than the 

 marble, which would interfere with the polishing, c. Verd-antique, or ophiolyte. d. 

 Micaceous, e. Tremolitic ; contains bladed crystallizations of the white variety of 

 hornblende called tremolite. f . Graphitic ; contains graphite in iron-gray scales dis- 

 seminated through it. g. Chloride; contains disseminated scales of chlorite, h. Chon~ 

 droditic ; contains disseminated chondrodite in large or small yellow to brown grains. 



2. Dolomyte. — Not distinguishable by the eye from granular limestone. 



3. Metamorphic Rocks, not Calcareous. 



Metamorphic rocks are made from the sedimentary rocks above enumerated by some 

 crystallizing process, and vary exceedingly in the perfection of the crystallization they 

 have undergone. Granite stands at one end of the series, and hard sandstones called 

 quartzyte, hard slates like roofing-slate, and partially crystallized limestones, at the 

 other; so that a distinct line between them and the sedimentary beds cannot always be 

 drawn. The rocks of most veins are similar in nature. Some chemically deposited 

 siliceous formations are included. 



The common ingredients are quartz, feldspar of different kinds, mica, of the species 

 muscovite and biotite, and sometimes also a hydrous mica, hornblende, pyroxene, talc, 

 epidote, chlorite, serpentine ; to which garnet, andalusite, staurolite, tourmaline, topaz, 

 and graphite may be added as characterizing prominent varieties. 



The rocks are described beyond in the following order : — 



1. Quartzose rocks, consisting chiefly of quartz. 



2. Mica-Orthoclase Series, or the Granite group. 



3. The Hornblende Series and Pyroxene Series, including Syenyte, Dioryte, etc. 



4. Garnet, Epidote, and Chrysolite rocks. 



5. Hydrous Magnesian and Aluminous rocks, including kinds consisting largely of 

 talc, chlorite, serpentine, pyrophyllite, etc. 



6. Iron -ore rocks. 



1. Quartzose Rocks. 



1. Quartzyte, Granular Quartz. — A siliceous sandstone, usually very firm, occur- 

 ring in regions of metamorphic rocks. It does not differ essentially from the harder 

 siliceous sandstones of other regions. Conglomerate beds are sometimes included. 



Varieties. — a. Massive, b. Schistose, c. Calcareous, d. Micaceous ("Greisen ") 

 or Hydromicaceous. e. Feldspathic, and sometimes Porphyritic. f. Gneissoid, it occasion- 

 ally graduating into gneiss, g. Tourmalinic, containing tourmaline. 



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