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H. W. TURNER 



Lawson/ as it is reasonably certain that at some depth below the 

 surface they all come together. The dikes vary from two inches 

 to two feet in width. Quartz veinlets, one with a convoluted 

 course, cut both the schists and the dikes. Between the dikes 

 and the ledge is a broken-up mass of the dike rock of a reddish- 

 brown color, penetrated by quartz veinlets and seams of dolomite, 

 and apparently in a fair way to form a lode, like that imme- 

 diately west, if the alteration should go farther. This mass 

 seemed a friction breccia and would indicate movement and 

 faulting along the lode. A microscopic examination of this 

 breccia showed it to be made up of fragments of the dike rock 

 cemented by dolomite and quartz. Throughout the rock, as 

 well as in the dikes just east, is scattered iron pyrite in minute 

 specks. The brown color is due to abundantly disseminated 

 limonite. The microscope shows the dike rocks, where not 

 replaced by silica and carbonate, to be composed almost 

 entirely of interlocking grains of soda-feldspar with some larger 

 twinned feldspars, in fact identical as to composition with other 

 similar soda-feldspar dikes. There thus seemed to be evidence 

 here that the dike rock has undergone replacement. To deter- 

 mine what alterations had taken place in the dikes some partial 

 chemical analyses were made as follows : 



PARTIAL ANALYSES OF SODA-SYENITE AND ITS REPLACEMENT 

 ALTERATIONS BY DR. H. N. STOKES 



1 American Geologist, Vol. XIII, p. 293. 



