334 THE PEjSTOKEE ILON-BEAlilNG SEHIES. 



which therefore are included by or closely encircle tlie feldspar, are chlorite, 

 sericite or muscovite (or both), biotite, probably kaolin, and quartz. In the 

 grains which have decoinposed to the greatest extent, the original feldspar 

 remaining and the mica and quartz most intricately interlock, so that an 

 examination with a moderately high power which covers only one original 

 individual of feldspar or a part of one gives the appearance of a com- 

 pletely crystalline rock in which the interlocking is of the most intricate 

 sort; yet when the same grain is examined with a low power its rounded 

 character is evident, and that the area is but an altered feldspar is manifest, 

 while the completely fragmental character of the rock as a whole is plain 

 at a glance (PI. xxxii, Figs. 2 and 3). 



The fragmental grains of quartz, although now unusually sharply 

 angular, often show with perfect clearness well rounded cores, their present 

 ano-nlarity being due to a renewed growth subsequent to their deposition 

 in their present resting place. Commonly the majority of the grains of 

 quartz are simjile, but at times many of them are more or less finely com- 

 plex, or even of a chalcedonic character. The (pumtity of this kind of 

 quartz varies greatly, rarely becoming almost or (juite as abundant as the 

 simple quartz fragments. In the interstices of tlie rock is found usually 

 a little finely crystalline quartz, which is of a secondary nature, as 

 plainly so as are the enlargements of the fragmental quartz grains. In the 

 simplest quartzose graywackes and graywacke-slates little else is present. 

 In these specimens it is evident that the induration which has often occurred 

 is caused almost wholly by the enlargement of quartz fragments and the 

 separation of finely crystalline quartz in the interstices, thus completely 

 filling the spaces which originally existed between the loosely piled frag- 

 ments and making the rock as compact and strong as though it were a 

 granite. The green and gray colors of the rock (in the absence of ferrite) 

 are due to the secondary products of the feldspar, chlorite, biotite, etc.; 

 green when chlorite, gray when muscovite and biotite are ])repondei'ant. 

 The original conditions and secondary changes of the simplest of the gray- 

 wackes are tluis clear. They were quartz-feldspar sediments, mingled in 

 places with a little clayey matter, perhaps also with a small quantity of 

 fragmental mica and some ferrite. They reached their 2)resent condition 



