STRUCTURAL OEOLOOY. 33 



The Kekequabie granite. ] 



iar hornblende porphyry (No. 741). At other times the hornblende is partly replaced by 

 augite, which is allied to aegyrine and in nearly all cases it can be seen to have been 

 derived from augite by a uralitic (?) alteration. This derivation is evinced chiefly 

 by a particolored polarization which sometimes represents exactly the original crystal 

 form of idiomorphic augite, surrounded by fringes or external growths beyond the 

 augite limits. When the augite grains were fragmentary, or -were corroded before 

 being enclosed in this rock, the hornblendic growths have exactly filled them out, 

 the dark color of the polarization (or even the color seen in ordinary light) showing 

 distinctly the original augitic .outlines. Besides the conspicuous hornblendes some- 

 times this schist contains traces of feldspars, but usually feldspar is not evident. 

 When feldspar is seen, the crystals often appear to have been altered into a micro- 

 granulitic mass of secondary grains which appear to be of quartz and feldspar. 

 Sometimes pellet-like spots appears under the microscope, which are occupied by 

 such granulation. By their assuming in thin section distinctly lighter and darker 

 aspects four times in one revolution of the stage they are plainly due to a replace- 

 ment of an old feldspar whose substance and crystalline integrity are not entirely lost. 

 The "groundmass" containing these altered crystals is composed largely of finer 

 condition of the same elements, but usually it embraces a notable amount of quartz. 

 This quartz is in the form of free grains, of angular clastic shapes, or it is very fine 

 and intimately interlocked with equally fine grains of feldspar. 



This green schist is sometimes composed almost wholly of actinolite spicules. 

 At other places it passes into a greenish graywacke. It is distinctly a fragmental 

 rock, and shows a coarse, even pebbly, structure, the pebbles being usually of rock 

 like itself, but finer grained. It is also distinctly bedded by sedimentation. It is 

 considered to be largely of the nature of a volcanic tuff, and grades into the green- 

 stones of the surrounding region supposed to be Upper Keewatin. This rock is 

 represented by many numbers, of which the following may be mentioned: Nos. 1409, 

 1411, 1412, 1413, 1768, 1049, 1050, 1055, 1057, 1060. 



This schist is part of a large sedimentary series, passing through greenwacke 

 and graywacke into a pebbly conglomerate with which it intergrades. This conglom- 

 eratic condition is sometimes specked with coarse white feldspars, when it has been 

 called porphyrel, and is well exposed in its perfect development at Zeta lake, east of 

 Kekequabie lake. This "porphyritic " aspect, however, is widespread and sometimes 

 appears in rock which is plainly fragmental though not conglomeratic, and has been 

 noted especially in the region between Moose and Snowbank lakes. 



The intrusive rock is sometimes a granite and forms distinct dikes cutting the 

 schist and its associates, and sometimes is a porphyry, forming knobs of small dimen- 

 sions that swell up rather fortuitously in the schists. As knobs this porphyry is 



