ELY GREENSTONE. 137 



when viewed from a distance, for the more acid granites. The macroscopic 

 textm-es commonly seen are the ophitic, the poikihtic, and the porphyritic. 

 The rocks possessing these textm-es vary from line-grained, almost aphanitic, 

 ones to those wliich are very coarse grained and, in exceptional cases, 

 have some constituents an inch and a half in length. The porphyritic 

 rocks have as phenocrysts feldspar or hornblende, or both, in a matrix 

 which vaj-ies from fine to coarse in grain. Some of the feldspar phenocrysts 

 are an inch and a half in length. Many of the finer grained forms of these 

 rocks ,are amygdaloidal and also frequently show beautiful cases of 

 spherulitic development. 



Good columnar parting is totally wanting in the greenstones of the 

 Vermilion district, but, apparently taking its place, ellipsoidal parting" is 

 abundantly present. All combinations of the above structures and textures 

 may be found in this complex and all gradations between the rocks 

 possessing them. Thus we find gradations from fine to coarse forms 

 and from the nonporpliyritic to the porphyritic. Those that are not 

 amygdaloidal at one place may become amygdaloidal elsewhere, and with 

 this change we may find the rocks becoming- porphyritic, possibly showing 

 ellipsoidal parting. Fine-grained ellipsoidal and spherulitic basalts grade 

 into coarse-grained ellipsoidal spherulitic basalts, or into coarse-grained 

 basalts that are neither ellipsoidal nor spherulitic. 



The greenstones are predominantly massive. Neverthel^s they show 

 the effect of dynamic action and are in many cases finely jointed. The 

 dynamic action affecting them has resulted in the production in several 

 places of very excellent friction breccias (reibungs-breccias) which can 

 with difficulty be separated from tufifaceous or conglomeratic deposits. On 

 the bare hills south of Moose Lake these basalts are in places brecciated, 

 producing rocks that strikingly simulate greenstone conglomerates. In 

 most cases the brecciated zone has a width of only a few feet. These 

 breccias might readily be mistaken for true conglomerates if the adjacent 

 massive rocks were covered and the breccias only were exposed. The 

 ellipsoids on great numbers of the exposures have very numerous and 

 prominent gashes which traverse them at various angles, though usually 

 nearly at right angles to the direction of -elongation. These are clearly 

 indicative of the mashing to which these ellipsoids have been subjected. 



«Mou. V. S. Geol. Survej- Vol. XXXVI, 1899, pp. 112-124. 



