104 AQUEOUS ROCKS 



Palseozoic varieties, and doubtless originated as did the flints 

 in the chalky limestones. Jasper is a dull or bright red, or yellow 

 variety of chalcedony containing alumina, and owing its color to 

 iron oxides. 



The name novaculite is given to a very fine-grained and com- 

 pact chalcedony, such as is suitable for hones. As commonly 

 used, the name is made to include rocks of widely different 

 origin, some of which are evidently chemical precipitates, while 

 others are indurated clastic or schistose rocks. The well-known 

 novaculites of Arkansas are clear white masses of chalcedonic 

 silica, containing scattering quartz granules, minute grains of 

 garnet, and numerous small rhomboidal cavities which seem- 

 ingly were once occupied by crystals of calcite or dolomite. 

 Opinions differ as to the origin of this rock. Owen^ regarded 

 it as a sandstone metamorphosed by percolating hot water. 

 Branner^ looked upon it as a metamorphosed chert; Griswold,^ 

 as a sedimentary deposit in the form of siliceous silt on a sea- 

 bottom, while Eutley^ argues that it is but a siliceous replace- 

 ment of beds of dolomite or dolomitic limestone. It seems 

 probable that the views of Branner or Rutley are the most 

 nearly correct. 



Quartz is a massive form of crystalline silica occurring in 

 veins, disseminated granules, and pockets in rocks of all kinds 

 and all ages. It is one of the most wide-spread and commonest 

 of minerals, and is often of a pink or rose color from metallic 

 oxides. Lydian stone is an exceedingly hard impure quartz rock, 

 of a black color and splintery fracture. It was formerly much 

 used in testing the purity of precious metals. 



(2) CARBOJSTATES 



Water carrying small amounts of carbonic acid readily dis- 

 solves the calcium carbonate of rocks with which it comes in 

 contact; on evaporation and through loss of a portion of the 

 carbonic acid, this is again deposited. In this way are formed 

 numerous and at times extensive deposits, to which are given 

 varietal names dependent upon their structure and the special 

 conditions under which they originated. Calc sinter or ttcfa is 



=^2d Eep. Geological Beconnaissance of Arkansis, 1860. 



* Ann. Rep. Geol. Survey of Arkansas, Vol. I, 1886, p. 49. 

 «Ann. Eep. Geol. Survey of Arkansas, Vol. Ill, 1890. 



* Quarterly Journal Geological Society of London, August, 1894. 



