Grenvitte A. J. Cole — Igneous Bocks of Stanner. 225 



naturally came to cover all augite-labradorite-chlorite rocks, of 

 whatever grain, i.e. (pre-tertiar}') altered masses verging on one side 

 into the diorite, and on the other into the (olivine) gabbro series. 



What, then, are we to do with the highly-crystalline representa- 

 tives of the augite-andesites ? It seems unnecessary to extend 

 Eucrite (augite-anorthite rock), if we can employ some more familiar 

 term. The bulk of the gabbros are, as Prof. Judd has shown, so 

 connected with the basalts, that we are still left with a gap, and into 

 this diabase has somewhat naturally stepped. Messrs. Hague and 

 Iddings x employ it in this sense, connecting, in their admirable 

 series of observations, diorite and hornblende-andesite, diabase and 

 augite-andesite ; and De Lapparent 2 also makes of his diabases a 

 series exactly parallel to his (hornblende) diorites. But the diffi- 

 culty of thus defining their position as distinct from diorite is shown 

 by Boricky's 3 use of diabase for hornblende-plagioclase rocks 

 where the former mineral can be shown to have been derived from 

 augite ; and the fact that many diorites are in this sense altered 

 diabases must lead to considerable confusion, 4 two parts of the same 

 mass retaining the same essential structure, and yet receiving different 

 names. 



Now Zirkel 5 has long ago given us a class of cmgite-diorites 

 distinguished from his diabase by containing oligoclase and not 

 labradorite ; , but now that the nature of the felspar no longer 

 restricts the diorites, this class becomes correspondingly extended 

 and fills admirably the vacant place. Augite and enstatite diorites 

 should seem no more strange than the corresponding varieties of 

 andesite, and the close relations of the pyroxenes and the amphi- 

 boles appear to support this comprehensive view, viz. that the 

 diorites form a natural group, containing now hornblende, now 

 mica, now augite, or now, as in the case of rocks at Stanner, two or 

 even three of these constituents. 



Diabase then remains much where Hausmann placed it, as a 

 common term for the more basic altered augitic rocks, without 

 question as to their age or much regard for structure. Not that 

 it is better in itself than " Greenstone," but that it is sanctioned 

 by more international usage. My excuse for dwelling thus far on 

 what may seem foreign to the mere description of the rocks of 

 Stanner lies in the fact that so many areas of augite-plagioclase 

 rocks (Augite-Diorites) occur upon our western border. Vague 

 and general terms are too valuable to be lost sight of in the 

 field ; but the use of an inexact name where another more closely 

 expresses an observed relationship can only be, and has been in 

 the past, a source of misapprehension and confusion. 



Many of the rock-sections above referred to have been made, and 

 the chemical work has been carried out, in the Geological Laboratory 

 of the Normal School of Science and Koyal School of Mines. 



1 Bulletin U. S. Geol. Survey, No. 17. 



2 Traite de Geol. 2me edit. p. 627. 3 Tscherm. Mittheil. ii. (1880) p. 78. 

 * See Hague and Iddings, Bull. U. S. Geol. Surv. No. 17, p. 21. 



5 Lehrbuch der Petrogr. (1866) ii. p. 7. 



DECADE III. TOL. III. — NO. V. 15 



