326 



G. P. MERRILL — DISINTEGRATION OF GRANITIC ROCKS. 



duced to yellowish brown shreds. The feldspars are in some cases 

 opaque through kaolinization, but in others are still fresh and unchanged 

 even in the smallest particles. The finest silt, when treated with a diluted 

 acid to remove the iron stains, shows the remaining granules of quartz, 

 feldspar and epidote beautifully fresh and with sharp, angular borders, 

 the mica being, however, almost completely decolorized and resembling 

 sericite more than biotite. An analysis of this silt yielded the results 

 given further on.* 



Column I shows the actual results obtained, and column II the same 

 recalculated to a water-free basis. In columns III and IV are given 

 the attempts to determine the soluble and insoluble portions of the same 

 silt. The soluble portion was that obtained by digestion, without fur- 

 ther pulverization, for two hours in h3^drochloric acid of one-fourth nor- 

 mal strength, the insoluble residue being treated for a like period with 

 carbonate of soda solution in order to extract the gelatinous silica set 

 free by the acid. This insoluble residue was in the form of a beautiful 

 fine, white sand made up of very sharply angular particles of quartz, 

 fewer feldspars, an occasional epidote and a considerable sprinkling of 

 almost amorphous material, in part kaolin and in part a gum-like sub- 

 stance, evidently representing a transitional stage of the feldspathic 

 alteration into kaolin. The analysis of the soluble portion is unfortu- 

 nately incomplete, owing to the cracking of a beaker and consequent 

 loss of a portion of the material. The insoluble residue from the two 

 grams treated amounted to 1.206 grams, or 60.3 per cent, and the soluble 

 portion by difi'erence to 0.7949 grams, or 39.7 per cent. 



Analysis of Silt. 



Ignition 



SiO,.,.. 



AlA-.- 

 FeA--- 

 CaO . . . . 

 MgO . . . 

 Na20 . . . 

 K,0.. . 



I. 



Actual 

 analysis. 



IL 



Recalcu- 

 lated. 

 Water-free. 



8.12 



49.39 



23.84 

 3.69 

 4.41 

 4.60 

 3.36 

 2.49 



99.90 



0.00 



53.74 



25.94 

 4.01 

 4.79 

 5.00 

 3.65 

 2.71 



99.84 



III. 



Soluble portion 



(39.7%). 



/ Extracted in HCI . . - . 2.83 

 I Extracted in Na^COg. . 28.08 



23.21 



11.26 



Undetermined 



J 



IV. 



Insoluble 

 portion 



(60.3 fo). 



1.61 

 61.85 



22.21 

 1.36 

 4.80 



traces 

 4.56 

 1.77 



98.16 



Unless otherwise stated, all analyses here given were made by the writer of this paper. 



