106 C. H. GORDON — SYENITE-GNEISS (LEOPARD ROCK) FROM CANADA. 



the appearance of a radiate structure. Usually a thin layer of the feld- 

 spar adjoining the pyroxene bands is finer grained than the main part of 

 the lump, but in some cases one or more large grains of microcline will 

 appear to lie directly against the pyroxene band. On close inspection, 

 however, they will be found to be separated by a very thin layer of fine 

 grained feldspar. A mass of the rock will sometimes show a thin seam 

 of the light colored constituent cutting across both pyroxene layers and 

 feldspathic ellipsoids. In may be traced across the latter by its lighter 

 color and finer grain. In specimen 150 a seam of this character cuts 

 entirely through the block, and apparently represents a fracture which 

 has been recemented by subsequent crystallization. 



The interstitial filling weathers more readily than the ovoid masses, 

 leaving sharp little trenches surrounding these on exposed surfaces. 



Beginning with a somewhat flattened ellipsoidal form, the feldspathic 

 masses become more and more flattened in one direction and extended 

 in a direction normal to it. With this flattening of the ellipsoids, the 

 pyroxene shells become thinner and arrange themselves more and more 

 in parallel bands until the ellipsoidal structure is more or less com- 

 })letely lost, and in its place there occurs a striped gneissoid rock consti- 

 tuting the third phase. On cross-fracture the pyroxene layers of the 

 latter are seen to coalesce, clearly indicating its relationship to the ellij)- 

 soidal rock. Where the rock incloses large crystals or masses of apatite 

 the ellipsoidal lumps arrange themselves more or less concentrically 

 about the inclosure, a feature which is characteristic also of the bands 

 of pyroxene and feldspar in the succeeding phase. This is well shown 

 in specimens 137, 146, 148, 154 and 158. 



STREA RED S YENITE-G NEISS. 



As the ovoid masses become more flattened and disk-like the augite 

 layers arrange themselves in parallel bands, alternating with the thicker 

 felds})athic la3'ers. Moreover, there is a marked diminution in the size 

 of the grains, while quartz becomes relatively more abundant. Here and 

 there areas appear which are coarser grained, and in these the pyroxene 

 is less abundant, and is disseminated in grains and small masses instead 

 of being aggregated into la3^ers. There is also observed occasionally in 

 the fine grained gneissoid rock large grains of feldspar, which sometimes 

 inclose grains of pyroxene. The masses of apatite inclosed in the rock 

 vary in size from a few inches to a foot or more across, and around them 

 the bands of pyroxene and feldspar curve concentrically. The apatite is 

 crushed in part or wholly to a granular, saccharoidal condition. Num- 

 ber 145 shows a portion of such an apatite mass in connection with the 

 adjoining rock. The latter is rather fine grained and is striped with 



