224 



DESCRIPTIVE MINERALOGY. 



Fig. 84. 



Fig. 8G. 



Fig. 87. 



Fig. 84, the contractee of Haiiy. g on i 112° 10'. 

 Fig. 85, unimixte of Haiiy. g on s 127° 52' 30" ; 5 on s' 116° 15' 5". 

 Fig. 86, trirhomhoidale of Haiiy. P on ?« 149° 2' 11" ; P on s 119° 2' 11" ; m on s' or 

 7»' on s 154° 39' 13" ; m on s or m' on s' 121° 32' 54". 



Fig. 87, soustractive of Haiiy. t on t 137° 39' 26" ; c on r or c' on r 152° 6' 52". 



Fig. 89. 



Fig. 88. 



Fig. 90. 



Fig. 88. The primary rhombohedron, with the lateral edges replaced by two planes. P 

 on r or ?-' 151° 2' 40". 



Also the twin crystals. Figs. 89 and 90. 



St. Lawrence Cotjnty. Probably no part of the world has furnished more beautiful or 

 interesting forms of calcareous spar, than the county just named. This will sufSciently appear 

 when I state that crystals have been obtained from nine to twelve inches in diameter, with 

 all the sides and angles perfectly finished. The usual colours of these crystals are white or 

 straw-yellow ; they vary from transparent to opaque. They occasionallj^ contain water or 

 some other liquid, but it soon disappears, as the specimens are very liable to be cracked 

 or broken by exposure to alternations of temperature. Mineralogists are indebted for the 

 fine crystalline forms of calcareous spar for which this county is so celebrated, to the mining 

 operations, which were commenced here in 1836, and actively prosecuted during the two 



