390 JULIEN 



hornblende, which makes up more than half of the rock, presents 

 in places the crystal outline proper to that mineral, proving that 

 it is not merely pseudomorphic but has crystallized as such. 

 The rest of the rock consists chiefly of a finely striated plagio- 

 clase ; but there is also some unstriated feldspar, which may be 

 orthoclase, and a few little interstitial grains of quartz are seen. 

 These last two minerals probably point to a certain impregna- 

 tion of the recrystallized basic rock by the granitic magma." 

 Other sections presented strings of magnetite granules and a 

 little brown mica. 



This description of a diorite schist, known to be directly 

 altered from a basic igneous rock, is almost a repetition of that 

 of the diorite schist of Manhattan Island,^ indirectly altered after 

 metamorphism. The points of difference are equally significant ; 

 the excess of quartz in the latter, from long-continued and 

 thorough pegmatitic impregnation : the state of the iron oxide 

 as hematite rather than magnetite, from the lower temperature 

 concerned in metamorphism : and even the partial separation of 

 bases, lime and iron oxide, represented by zoisite and hematite, 

 probably from the same cause. 



On occluded masses of igneous material, the processes con- 

 cerned have been of two kinds, mechanical and chemical. 



Mechanical Processes Attending Occlusion. — The following 

 are the chief effects, as shown on Manhattan Island, of mechan- 

 ical processes due to agencies of pressure, deformation and 

 shearing. 



Flattening into lenticular discs with thin tapering edges ; the 

 pegmatite occlusions in particular breaking up into small nodules 

 and lenses, a few inches in length. 



Crumpling and corrugation by tangential pressure, in the 



1 A. A. Julien, " Genesis of the amphibole schists and serpentines of Manhattan 

 Island, New York," Bull. Geol. Soc. Am., XIV, 1903, 427-439 The present 

 paper, which is a further development of the same subject, offers the opportunity to 

 record the following corrections to the former : 



Page 461, 4th line. For " .']Z<^\\/7i^~^'a,'' read " d^.'' 



Page 465, last column, 3d line. Same correction. 



Last column, last line. For "^/''," read " ^/^^." 



Page 492, 5th line. For " paucity," read "poverty." 



