150 THK PKNOKEE IKON BEARING SERIES. 



amount of rouiidiuii' appears to be in a direct relation to the siz(^ of the 

 piirticles, the more minute pieces liaving- remained quite anguhu\ In 

 speakinjj- of these pitM-es as rounded, however,' we refer always to the 

 original fragments, whose outlines for the most ])art still remain distinct; 

 but as tlle^■ now stand, a large proportion of them an^ Ijuilt out by second- 

 ar^' enlargement; the adih^l portions varying greatlv in width, but often 

 extending bevond the original fragments ii distance equal to a fifth or sixth of 

 their diameters. Th(^se enlargements are, as usual, opticallv continuous with 

 the original fragments, and have frequentlv interlocked with one another 

 in such a fashion as to produce very irregular outlines. It is noticed that 

 these secondary" enlargements are narrowest in those sections which have a 

 considerable quantity of brown iron oxide among the interstitial materials. 

 The outlines of the original quartz fragments where the\' have received 

 enlargements are em[)hasized, as is usual in such cases, b\' particles of 

 brown iron oxide, and bv the presence of minute cavities. In a few cases, 

 juino-led with tliis lirowii ii-on oxide, and at times almost excluding- it, are 

 films of a greenish clilorite. 



The feldspar fragments include three distinct kinds. The most 

 abundiuit is unstriated, and its appearance is, in everv respect that of the 

 ordinary orthocla.se of the granitic rocks, and there can be no reasonal)le 

 doubt that it is of this nature. The difficulty of sejiarating these supposed 

 orthoclase particles tVom the other ingredients of the rock, particularh' from 

 the microcline, would be so great that it is not thought wortli while to make 

 the dct(MMiiination an\" more certain than this. A .second vai-ietv is the 

 ordinary cross twinn('(l microcline, and the tliii-d is a .striated plagio- 

 clase. On making man\- measi;reinents of the extinction angles of the 

 last named variet}- by Pumpellv's method, we fail to' find anv angles 

 wluch would suggest the presence of a plagioclase more basic than one 

 belonging in the oligoclase series. We may therefore, with some confi- 

 dence, say that the feldspar particles of these rocks include pieces of ortho- 

 clase, microcline, and albite or oligoclase, or both, an association which is 

 that of the ordinary granites. Often the.se feldspar iVagments are very 

 f're.sh, but in other cases manv of them are nuich altered or decomposed, a 

 gradation in this respect being foun<l to obtain between those kinds in 



