118 C. H. GORDON — SYENITE-GNEISS (LEOPARD ROCk) FROM CANADA. 



visible on a transverse fracture face. Specimen 15G (186), taken from the 

 dump, represents the same structure in a freslier rock. The constituents 

 appear in a remarkably fresh condition. The felds})athic areas have 

 been completely flattened, so tliat on a fracture face parallel with the 

 plane of the greatest and least axes of the flattened ellipsoids the con- 

 stituents are seen in parallel bands. When the rock breaks transverse to 

 this and the augite bands, the latter are seen to coalesce. The mass of 

 the rock is fine grained, with large cr^'-stals of microcline scattered here 

 and there along the feldspathic bands. 



Under the microscope the rock is seen to consist chiefly of finely granu- 

 lar feldspar, with larger grains of feldspar and augite scattered through 



the groundmass. The granular 

 groundmass consists of microcline 

 and unstriped feldspar, the latter 

 occurring both as a cement and 

 in small grains carrying numer- 

 ous nodular (piartz inclusions. A 

 small amount of striped feldspar 

 is also present. 



The granular microcline gener- 

 ally a])pears fresher than that in 

 large grains, and in some cases ap- 

 pears more cloudy at the center 

 than in the peri])heral [)orti()ns. 



The augite grains vary greatly 

 in size, but in general are inter- 

 mediate in size between the micro- 

 honibicii.k-; ('line of tlic grouudiuass and the 

 large porph3'ritic grains. They 

 lie scattered along planes in alternation with the bands of feldspar. 

 Hornblende is present in considerable amount, associated with the augite. 

 It does not occur outside of the augite bands. Its relations to the augite, 

 however, are not such as to clearly i)rove its derivation from that mineral, 

 it sometimes api)ears in small flakes along the cleavage lines of the augite 

 and is frequently in zonal relation with the latter. It shows the relations 

 with the other constituents characteristic of the micropoikilitic structure, 

 and frequently appears in crystals with characteristic crystallographic 

 outlines. 



In figure 8 it is evident that the hornblende is the result of a separate 

 crystallization, as sliown l)y its idiomorphic form and relation to the 

 adjacent minerals. The manner in which it incloses the apatite shows 

 that it has crystallized subsequently to the apatite. Moreover, its i)er- 



FiGURK ^.—/ilinnioi f>/iir Ilo) tihlcmir Crystal iu lit 

 streaked Syriiitr-i^iiriss. 



Ap = apatite; An = avi^itc ; // 

 7"=titanite; TV/ = microcline. 



