PETEOGRAPHICAL CBARACTEES OF ARCHEAN. 41 



of the quartz, unless such quartz represents the "quartz de corrosion" of 

 the French authors, continued through the entire time occupied by the crys- 

 tallization of the feldspars, since it is included in the oldest feldspar of the 

 rocks, and also forms the matrix in which lie the youngest feldspars' Undu- 

 latory extinction, so general in the quartzes, shows that the rocks have been 

 subjected to pressure, and in some cases it has been sufficient to produce 

 the extreme cataclastic structure of very greatly mashed rocks. 



The quartz includes numerous gas and fluid inclusions, the latter 

 frequently with dancing bubbles and forming negative crystals, by means 

 of which it is easy to orient the irregular grains. The quartz of one of the 

 specimens was found to contain liquid inclusions, each of which, besides the 

 usual bubble, held a small rectangular crystal. These crystals are trans- 

 parent, with a light greenish ting*e. A crystal similar in appearance found 

 in the same quartz individual is partly inclosed hj a large (j -shaped bub- 

 ble, and gave inclined extinction, though no further optical tests could be 

 made upon it. 



Three kinds of feldspar are present : (1) A finely striated plagioclase ; 

 (2) a feldspar, unstriated, or at most showing Carlsbad twins, and presumed 

 to be orthoclase ; and (3) microcline, these last two being frequently inter- 

 grown after the manner of perthite. The plagioclase was the first feldspar 

 to crystallize. It is invariably so altered that the twinning laminse are 

 nearly obliterated, thus preventing accurate measurements. It is probably 

 oligoclase; and if so, it is highly probable that much of the white mica 

 produced by its alteration is paragonite instead of muscovite, a fact not 

 determinable microscopically. The phenocrysts are orthoclase, usually 

 in Carlsbad twins, and thus at first sight appear to have been the first feld- 

 spar to crystallize; but I find that these phenocrysts not uncommonly 

 inclose small rectangular, more or less automorphic,^ crystals of plagioclase, 

 which is in reality the oldest feldspar. Hence these orthoclases, notwith- 

 standing their porphyritic character, are later than a jDart of the plagioclases. 

 One phenocryst with Carlsbad twinning was observed in which one part of 



' Automorpli, Xenomorph; Uber die Eruptivgesteine im Gebiete der Schlesisch-Maebriscbeu 

 Kreideformatiou, by Carl E. M. Eobrbacb : Tseb. Miu. Pet. Mit., Vol. VII, 1886, p. 18. 



Idiomorpb, AUotriomorpb; Rosenbusch: Mik. Phys., Vol. II, 1887, 2d ed., p. 11. 



L. V. Pirssou bas leceutly proposed in a paper, read before tbe Geological Society of America, 

 on A Needed Term in Petrology, the term anbedra for minerals which do not possess crystallograpbic 

 outlines and are xeuoraorpbic, in contradistinction to those which we properly call crystals and which 

 are automorpbic : Geol. Soc. Am. , Vol. VII, 189(3, p. 492, and Am. Jour. Sci., 4th series, Vol. II, 1896, p. 150. 



