G. H. Williams—Pyroxene and Hornblende. 265 
___ Microscopic sections of gabbros from Eagle Harbor, Ash- 
_ land Co., Wisconsin, the possession of which I owe to the kind- 
_ ness of Professor R. D. Irving, show the undoubted change of 
_ the pyroxene into single individuals of compact brown horn- 
_ blende, as recently described by him,” although in none that I 
_ have examined is the change as plainly exhibited as in the rocks 
_ from Montrose Point. The wernerite-hornblende rock, in con- 
nection with which the apatite deposits of Scandinavia occur, 
ave been recently studied by H. Sjégren,” who called them 
_ dipyrediorites. They are regarded by this author as a peculiar 
_ facies of a gabbro, formed from this by the paramorphosis of feld- 
_ Spar to wernerite and of pyroxene to hornblende. B 
and green hornblende are produced in this way. I am indebted 
_ to Mr. Frank D, Adams, of the Canadian Geological Survey, for 
_ the opportunity to study a series of sections of both the Swe-. 
dish rocks and others exactly like them, occurring in connec- 
_ tion with the apatite deposits near the Ottawa River in Canada. 
_ All of these show the gradual change of pyroxene to compact 
4 ig hornblende in a manner closely resembling that exhibited 
_ by the Cortlandt rocks. 
__ The so-called “black granite” from Addison, Me., seems to 
have originally been an augite-plagioclase rock containing 
_ Some biotite. The augite, however, is to a large extent under- 
_ are not accidental but must always be in accordance with the 
ced. 
o such a 
_ €xXistence of the other, then the molecules are no longer ina 
‘ Geology of Wisconsin, vol. iii, 1880. Third An. Report of the Director of 
: vad oy Bronte Survey, p. 105. Copper-bearing Rocks of Lake Superior. Mono- 
Pp J 
™ Geol. Féren. i Stockholm Forh., 1883, vi, 447. Cf. Neues Jahrbuch fiir Min., 
_ Ste. 1884, I, ref. 81. 
