OF ARKANSAS. 



177 



As no carbonic acid determination was made, it remains undecided 

 whether the oxide of zinc occurs in the rock as such, or in combination 

 with carbonic acid; most likely as a basic carbonate. 



-o- 



The foregoing analyses need no comment. Nos. 32, 33, and 34 are 

 true dolomites; the small amount of carbonate of zinc, which occurs in 

 two of them, is by no means surprising if we consider that the deposition 

 of carbonate of zinc in the crevices of the rock was most likely effected 

 by means of liquids containing the salt of zinc in solution; and whether 

 these liquids actually percolated through the dolomite or entered the 

 crevices by some other way, the deposition of a small quantity of the salt 

 in the immediately adjoining rock is equally well explicable. Gustav 

 Bischof mentions several instances of this kind {Elements of chem. and 

 phys. geology. Engl, edition, vol. 1, p. 165.) 



LIGNITES. 



Both varieties of lignite, the analyses of which are given below, occur 

 in the same bed, interstratified in the quarternary deposits of Crowley's 

 ridge, Greene county. 



No. 38. Lignite, from the Beech-branch of Cache, near Gainesville, 

 Greene county. 



Color light brown to blackish-brown; woody structure eminently pre- 

 served, laminated; on fracture, partly shining, partly dull; may be cut with 

 a knife, cut surface shining; very brittle; on application of a gentle heat, 

 evolves empyreumatic odor and assumes the appearance of charcoal. 

 Composition, dried at 212 to 220 deg. F: 



Volatile matter 41.030 



Fixed carbon (charcoal) 57.405 



Ash 1.505 



100.00 

 The air-dried lignite lost 14.89 per cent, of moisture at 220 deg. F. 

 A qualitative examination of the ash showed the presence of clay and 

 silica, sulphate of lime, iron, alumina, and potassa. 



12 



