PETROGRAl'HIC GEOLOGY AND DESCRIPTIONS. 505 



Gabliro. Dioryte.] 



k. "These pinkish beds and seams, which simulate planes of bedding, 

 are probably due to near contact with the underlying formation and infusion from 

 it." There are two rocks represented by this number, although doubtless from the 

 same place and closely related; one is the above tine-grained granite, which may be 

 a recomposed acid debris (or graywacke), and the other is a coarser phase of the 

 " intermediate " or contact rocks, a basic irruptive permeated by acid elements, 

 showing granophyric structure, though mainly still of basic character. (Compare, 

 also, rock No. 707.) K. H. w. 



No. 707. GABBKO. (AltemL) 



"In some places in the trap, where one of these red seams (No. 700) passes through it, the hornblende, 

 which accompanies the red rock, greatly preponderates, or is very coarse and sometimes is fibrous and radiating. 

 coating the walls of the seam. In such places mica also can be seen, and also, mixed with the fibrous horn- 

 blende, occasionally a crystal of quartz." 



Ref. Annual Report, x, page 83; Bulletin ii, page 87. 



A medium-grained, granitoid rock of a dark greenish-gray color. The 

 rock is composed of gray feldspar and considerable quantities of dark minerals, 

 among which can be recognized biotite, magnetite and fibrous hornblende. 



Mic. The section shows a gabbro which has been considerably altered. The 

 minerals are plagioclase, niijitc, nini/iiffitc, hornblende, ch/urite, yt/rtz, bivtitr, l.<>linH<> 

 and (qifttitc. The plagioclase, augite, apatite and part of the magnetite appear as 

 original minerals, and the others as secondary. The augite shows the diallagic 

 parting well developed and it has largely altered to fibrous hornblende and chlorite. 

 The apatite is in grains of considerable size. 



One section examined. 



Aye. Cabotian. u. s. G. 



No. 708. DIORYTE (ivith quarts). 



Portage between Mayhew and Loon lakes; near the centre of the S. W. % sec - 36, T. 65-3 W. 

 Ref. Annual Report, x, pages 83, 86; Bulletin ii, page 118. 



Meg. A rather fine-grained rock, greenish-gray in color and composed of white 

 to pinkish feldspar and considerable hornblende. Reflections can be obtained from 

 areas of small size, thus giving a lustre-mottled appearance to the rock. 



Mir. The section is composed mainly of fe/</x/><ir and hornblende. The former 

 mineral is rather weakly polarizing and is considerably altered, kaolinite, iiinKcorife 

 and chlorite being developed in it. It is mostly untwinned, but a few grains show 

 albite twinning. The uniformly low extinction in the twinned sections, as well as 

 in cleavage fragments, indicates that the feldspar is mainly D/iyorlnxe or ofif/orlase- 

 timli'xhie, although this determination is not as certain as might be desired. This 

 mineral occurs in rather large irregular grains making up the background of the 

 rock and including the other minerals in a somewhat poikilitic manner. 



