PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 



715 



Eaterfllyte.] 



Mey. The hand sample consists of some of the esterellyte and some fine-grained, 

 hard, greenish graywacke. The latter is probably a fragment included in the former, 

 although from the hand specimen and the field description this point is not clear. 

 No section. 



I Age. Archean (Keewatin ). r. s. G. 



No. 1399. ESTERELLYTE. 



From the knob, southwest corner sec. 29, T. 05-ti, Kekequabic lake. Taken from the weathered surface. 

 Compare Nos. 1061, 1062, 1094, etc. 



fief. Annual Report, xvi, pages l(K), 124. 



M>'!/. Coarsely porphyritic with feldspar and more finely porphyritic with pyrox- 

 ene. Shows pebbly forms. 



The gray porphyry (No. 1094) at the southwest corner of sec. 29, T. <>"> i, rises about 100 feet above the 

 hike, and composes the whole peninsula, making a knob by itself. It is very siliceous (No. 1IJ98). It is massive, 

 or coarsely jointed. The feldspar crystals are not always perfect in form, but approximate a true crystalline 

 shape. They seem to be of orthoclase. They weather red. The long exposed (or at least the burnt) surface of 

 the whole rock becomes reddish, but the surface scales off by tire and keeps a fresh gray color exposed. There 

 is in some places a prevailing direction that of the general strike - seen in the longer axes of the crystals. They 

 are also apt to stand vertical, edgewise, in the same direction. In the rock are boulder forms. These are most 

 frequently of greenstone, and then they are not porphyritic, but sometimes they are of some rock which weathers 

 a pinkish-red color. They are also of a siliceous gray rock, resembling the matrix of the porphyry, but liner 

 grained, and also of other light-weathering kinds. But in the main this is a homogeneous rock. These boulder 

 forms are by no means a common occurrence, at least at this place. Yet, in other places, there is a various 

 distribution apparent in the crystals. They are either more conspicuous and more numerous, or else less 

 frequent, in rounded spots: or they stand out at different angles, as if they had been dependent on the varying 

 nature, position, structure or grain of the enclosing rock. This distribution and confused arrangement are so 

 combined as to bring out to view indistinct outlines of former included boulders. From this I conclude that 

 the whole rock is a modified condition of the sedimentaries here prevalent, and that it indicates what would 

 become of the whole formation (conglomerate, graywacke, slate, chert, etc.), if under similar conditions the 

 rearrangement and recrystallization had been carried to completion a syenyte or a granite, at least an acidic 

 rock. Here there is no basic surplus to give the rock a doleritic aspect. Where this has been the case the 

 singular "ambiguous greenstone" has apparently been the product, a kind of fragments! basalt. 



In one 



Mic. The much-twinned feldspars are conspicuous and remarkable, 

 instance one of these crystals embraces completely one 

 of the pyroxenes. This is, however, a rare structure. 

 Usually the crystals of the porphyritic elements 

 are wholly independent. Sometimes quartz figures 

 amongst the large elements in a granophyric manner, 

 but in general it is confined to the finer groundmass 

 in which it is granulitic with feldspar. 



It is very difficult to decide from optic properties 

 what is the species of the feldspar. Several observa- 

 tions make it certain that >< K is in the acute bisectrix, 

 and hence the mineral is optically positive. The optic 

 angle is also small, comparatively, being nearer to 

 that of anorthoclase (45) than of any of the feldspars. 

 On such an index of elasticity, extinction (on indistinct cleavage) -is 4 to 5 



Section otligue to 010, showing tht 

 positions of /Vg and Np in the prin- 

 cifal part of the cc>/etal. 



FIG. 44. JEGYRINE-AUGITE IN NO. 1399. 



The 



