1866.] MACFARLANE — ON CUPRIFEROUS BEDS. 11 



Lime 1.57 



Magnesia 30 



The residue consisted of the same dark and light coloured parts 

 as in the case of the rock first described. Calculated in the same 

 manner as it, the mineralogical composition of this rock from the 

 Quincy adit would be 



Delessite 42.60 



Labradorite 50.69 



Pyroxene or hornblende 5.62 



Magnetite 1.09 



100.00 

 From the particulars above given, it would seem that the consti- 

 tuents of the traps of the Portage Lake district are principally 

 feldspar of the labradorite species, and chlorite of a species allied 

 to delessite, with which are found occasionally mica, small quan- 

 tities of magnetite and perhaps of augite or hornblende. Similar 

 results are given in Foster and Whitney's Lake Superior Re- 

 port II, 87 ; but the relative proportions of the constituents 

 are not given, nor is the peculiar nature of the chlorite referred to. 

 The name of greenstone would seem altogether inapplicable to 

 these rocks, because augite or hornblende only occurs in them occa- 

 sionally if at all, and then in comparatively small quantity. As to 

 the name of trap, the rocks previously so called have been by the 

 best lithological authorities subdivided into two families, Mela- 

 phyre and Basalt.* The latter family which includes dolerite, 

 anamesite and common basalt is distinguished by the dark, mostly 

 black or greyish-black colour, the high specific gravity, and the 

 richness in augite and magnetite of its rocks, and by the frequent 

 occurrence in them of olivine and zeolites. The melaphyres on 

 the other hand are characterised by their apparent want of augite, 

 by their comparatively low specific gravity, by their colour of red- 

 dish-grey mixed with green and black, and their frequent deve- 

 lopment as amygdaloidal varieties ; in which case quartz, calcspar and 

 delessite fill the cavities more frequently than zeolites. The traps 

 above described would seem to belong to the class of melaphyres, 

 and to resemble especially those of Mansfeld described by Freies- 

 leben, of Saxony,f and that of Faucogney described by Delesse. 



* Naumann ; Lehrbuchder Geognosie i, 599 ; Senft. Classification und Bes- 

 chreibung der Felsarten. pp. 262 & 272. 

 f Geognostische Beschreibung des Konigreiches Sachsen ii, 447. 



