218 GEOLCGICAL HISTORY OF LAKE LAHONTAN. 



solution became finally white. When some of the crystals were placed on 

 a glass slide under the microscope, and then water poured upon them, it was 

 observed that they for a moment were completely transparent and under- 

 went no change ; soon, however, the surface became clouded, and then a 

 granular separation took place gradually. As the CaCl2 was dissolved they 

 entirely lost their transparency, and finally there remained only a skeleton of 

 calcium carbonate corresjwnding in form and size to the original crystal. These 

 fell to pieces when touched, and there resulted minute spherical masses of 

 probably amorphous carbonate. This salt was found to have the composi- 

 tion 2CaC03+CaCl2+''H30. The crystals were shown by v. Kokscharof to 

 belong either to the orthorhombic or monoclinic system. It is. not to be 

 supposed that this salt of Fritzsche is in any way an explanation of the 

 thinolite enigma, and yet his observations are of great interest in this con- 

 nection. In order to complete the subject the fact may be noted that Ber- 

 thier speaks of forming a compound of calcium-carbonate and chloride by 

 fusion. 



"Another hypothesis may be ofi"ered as to the composition of the orig- 

 inal mineral, viz: that it was a double salt of calcium and sodium, perhaps 

 conforming to the formula CaCOa+NaCl, or better CaC03-|-2NaCl, which, 

 it is possible, might also be isomorphous with phosgenite. This is so purely 

 hypothetical that very little weight can be given to it ; still it may not be 

 entirely useless to throw out the suggestion, although various serious objec- 

 tions at once come up to mind. In any case it must be borne in mind 

 that carbonates and clilorides were the salts most likely to be precipitated 

 from the lake water, and calcium and sodium were the prominent basic ele- 

 ments at hand." 



The crystals deposited on such an enormous scale in Lake Lahontan 

 are considered by Professor Dana as being of the same nature as the well 

 known Sangerhausen pseudomorphs Similar crystals have also been found 

 at other localities, but for the discussion of these mineralogical relations we 

 must refer the reader to Professor Dana's report, where these matters are 

 considered at some loiigth. 



