i 4 4 A - F - BUDDINGTON 



the quartz-pyrophyllite or quartz schists are so intimately inter- 

 woven that all may be treated together. 



The proof that these rocks have originated through replace- 

 ment is based on the following data: (i) the preservation of the 

 structures of the primary rock in the secondary rock, (2) the pres- 

 ence of unattached and unsupported portions of the country rock 

 within the replacement products, (3) the introduction of large 

 quantities of some elements and the solution of others without any 

 notable change in volume or porosity, (4) gradational contacts, 

 and (5) the massive homogeneity of all the rocks, and especially 

 of the pyrophyllite, which does not show the foliated crystalline 

 structure so characteristic of pyrophyllite veins which fill pre- 

 existing fractures. To quote examples which belong to the first 

 category, we find. the following structures preserved in pyrophyll- 

 itized rhyolite: (1) flow structure, (2) spherulites, (3) pebbles of a 

 partially replaced conglomerate, and (4) perlitic structure (Fig. 5) ; 

 these in the quartz-pyrophyllite rocks: (1) spherulites and (2) 

 breccia structure; the following in pyrophyllite: (1) fragments 

 of volcanic breccias, (2) pebbles of conglomerates, and (3) spheru- 

 lites; while in the pinite and pinite schists we have preserved 

 spherulites, traces of flow structure, axiolites, microspherulites, 

 and perlitic structure (Fig. 6). Additional evidence of replace- 

 ment is found in the inclusions and stringers of country rock 

 within the pyrophyllite veins and the intimate manner in which 

 the two are often intermixed. Not only this most convincing 

 field evidence but chemical considerations prove almost conclu- 

 sively that these rocks must have originated through replacement 

 of rhyolite or rhyolitic volcanics. 



From a study of the foregoing field and chemical evidence, con- 

 clusions have been drawn as to the genetic relationships of the 

 eight different rocks described under "Chemical Analyses" and 

 "Petrography," and as to the succession of processes which pro- 

 duced them. This relationship is graphically represented by the 

 following diagram, in which the numbers refer to the chemical 

 analyses given under "Chemical Analyses," which may be taken as 

 typifying the composition of the respective rocks: 



