THE NATURAL HISTORY SURVEY. 5! 



lustre. These two directions of perfect cleavage assist mate- 

 rially in the orientation of a crystal. There are two other 

 directions of incomplete cleavage, one parallel to the orthopin- 

 acoid and the other parallel to the steep orthodome (103). 

 The hardness of gypsum is 1.5 to 2.0. The specific gravity is 

 2.3, lustre parallel to the clinopinacoid, pearly and shiny, par- 

 allel to other surfaces subvitreous, massive varieties dull, color- 

 less, white, brown, yellow, blue; streak white; transparent to 

 opaque. Yields water in a closed tube, fuses easily at 3 in the 

 scale of fusibility, coloring the flame a reddish yellow. Heated 

 to a temperature not above 260 C forms plaster of paris, which 

 upon moistening with water again becomes solid. Soluble in 

 hydrochloric acid. These crystals were formed by the decom- 

 position of the marcasite in the clay probably in a manner 

 shown by the formula Fe S 2 +CaCO 8 +3 H 2 O-f7 O==CaSO 4 ' 

 2H 2 O+FeCO 8 +H 2 S0 4 . 



Melanterite. FeSO 4 +7H s O. Monoclinic. 



This sulphate is a direct result of the oxidation of iron 

 sulphide in the presence of water. Commercially it is known 

 as copperas, or iron vitriol. The crystals observed in the 

 museums where iron sulphides are gradually disintegrating 

 are usually fibrous, capillary and stalactitic at first, and 

 subsequently, by drying, pulverulent. Fracture, conchoidal; 

 brittle; hardness 2; specific gravity, 1.89; luster vitreous; 

 color, green, yellowish on exposure, white; streak uncol- 

 ored; subtransparent to translucent. Taste, sweetish, astrin- 

 gent, metallic. Easily soluble in water; melts in its water of 

 crystallization, leaving behind a white mass which, when 

 roasted before the blowpipe, yields red iron oxide. 



CLASS VIL SALTS OF ORGANIC ACIDS. 



This small and unimportant class is not represented in this 

 region. 



CLASS VIIL HYDROCARBON COMPOUNDS. 



Of the HYDROCARBON COMPOUNDS there are at least four 

 representatives. 



Natural Gas. 



At various places in the vicinity small quantities of natural 

 gas escape from wells, cellars, and other excavations. At 

 Edgewater a gentleman capped his drinking water well, 



