THE PALMEK GNEISiSES. 



217 



gTanitic y-raiiis of feldspar in tlie least altered of the gneisses, stronii'ly 

 suggest that these rocks are very schistose granites in wliicli the alteration 

 of the feldspars has proceeded so far as to destroy their original ontliiics and 

 to yield a uniform aggregate of decomposition products. The desti-uction 

 of the outlines of the original grains is as much due to the mashing to 

 ^vllic]l tlui rocks have been subjected as to the alteration they have suflPered, 

 and the completeness of the alteration must itself be due largel)' to this 

 same mashing', which fractured the feldspars of the l)()rder granites and 

 rendered them more easy preys to the attack of decomposition processes 

 than the same minerals in the more massive granites beyond the limits of 

 the peripheral zone of maximum movement. 



An analysis of one of the most schistose phases of the Palmer gneisses, 

 specimen No. 20647, from the top of the large hill in the NW. ^ sec. 35, 

 T. 47 N., R. 26 W., ^vas made by George Steiger, of the Survey laboratory. 

 His results are as follows: 



Analysis of Palmer gneiss. 



SiOj 



TiO: 



ALO:, 



Fe.O, 



FeO 



Mn< ) 



CaO 



MgO 



K,0 



Na.O 



H. Oat 100-.... 

 H.O above 100'^ 

 PsOs 



Total ... 



82. m 



.14 



11.32 



.97 



.26 



iSoue. 



.17 

 1.04 



.59 



.18 

 2.33 



.09 



99.69 



These figures correspond very nearly to those that would be obtained 

 upon analysis of a mixture comj)osed of 68.6 per cent tjuartz, 14.6 per cent 

 kaolin, 8.7 per cent sericite, 6.7 per cent plagioclase (0.6 per cent anorthite 

 and 5.1 per cent albite), 1.2 per cent chlorite, 1 per cent magnetite, and 



