Minei^alogy and Geology of the White Mountains. 117 



seemed to be undergoing this change, we must look for another 

 and more silent cause. This must be found in frost, moisture, 

 &c., operating especially upon the large proportion of feldspar, 

 the alkali of which is removed, and the mass is thus rapidly dis- 

 integrated. The masses exfoliate on their angles and curves, and 

 it is not uncommon to meet with those that seem to be affected 

 by what Dolomieu calls la maladie du granite, which, on being 

 struck with a hammer, fall entirely in pieces or grains. The ex- 

 tent of this process may be imagined from the fact, that from 

 Bartlett to the Notch, (nearly thirty miles,) the surface of the 

 ground (as cut by the road ditches) seems entirely made up of 

 decomposed feldspathic granite sometimes to the depth of two feet. 



Octahedral Fluor Spar. 



Half a mile above the tavern of the elder Crawford, in the 

 ruins of a slide east of the Saco, this rare mineral is found, which 

 was mentioned twenty eight years ago in Bruce's Mineralogical 

 Journal ;* but the difficulty of obtaining specimens is much less 

 than formerly. The spar is found in masses of radiated quartz, 

 easily broken ; and occurs in pale green octahedra, from one fourth 

 of an iDch to one inch and one fourth in diameter, but is easily 

 fractured in breaking the gangue ; it phosphoresces most beau- 

 tifully, on hot iron, with at first a yellowish light, which be- 

 comes finally of a peach blossom color. On ascending the gorge 

 about five hundred feet, (here about ten feet wide,) the quartz is 

 found in place, on the south side of it, in close contact with the 

 granite, which on the other side is removed, forming a vein or 

 dike, {for it is really one, ) two feet wide, and continuing farther 

 up the mountain. Its structure is drusy, and there is near the 

 middle a double serrated line, formed by the interlocking of quartz 

 crystals. By unknown causes, the fluor has been in many cases 

 partially or entirely removed, and the cavities thus formed are now 

 filled with quartz in plates and crystals. Such a phenomenon in 

 calcareous rocks and veins would be easily explained. The 

 fissure existing, the calcareous matter in solution is deposited on 

 either side, till the drusy surfaces unite in the middle. What 

 greater difficulty in applying the same solution to deposits of sili- 

 ceous matter in veins? The fluor is not equally disseminated 



* Mineralogical notice respecting American fluates of Lime : by the Editor, 

 Bruce's Min. Jom., p. 33, Jan. 1810. 



