1899] Mineral Resources of the Ottawa District. 17 



Laurentian or Huronian, and over the origin and relations 

 of which many wordy battles have been waged, consist of gran- 

 ite, gneiss, limestone, greenstones, &c. The term gneiss does 

 not apply of necessity to rocks of any special age, but has 

 a general reference to structure only, though this distinction has 

 often been lost sight of in discussions on the subject. A gneiss 

 has been by some regarded as peculiar to the rocks of the 

 Laurentian system, yet when we find a granite of comparatively 

 recent age, as is the case of many of the masses which 

 penetrate the sedimentary formations as recent as the Cretaceous, 

 assuming a foliated structure, especially on the outer zone, 

 a feature which may be due to pressure or other causes, it is 

 also styled a gneiss, as readily as is its older brother of the 

 Laurentian time. 



The generally accepted idea at the present day, as to the 

 structure and relations of these oldest rocks of our country may 

 be briefly stated, as these points have a manifest bearing on the 

 question of mineral deposits. The lowest, and presumably the 

 oldest; since upon these all the others rest, is a reddish, or greyish 

 granite gneiss but containing different coloured bands, and called 

 for the purpose of distinction, the lower or sometimes the 

 Ottawa gneiss. This rock may be held to represent the oldest 

 known crust of the earth, though probably now in a form much 

 modified or altered from its original condition, when this crust 

 was first consolidated. It is, in so far as yet known, lacking 

 in mineral deposits of economic importance. 



Succeeding this in ascending order, are certain other 

 gneisses of greyish or darker shades, some of which have been 

 clearly shewn to owe their origin to aqueous action, though now 

 in a highly metamorphic state. With these are associated bands 

 of quartzite and limestone which sometimes form large areas. 

 These last, with the upper gneisses, form what has been styled the 

 Grenville and Hastings series of the Ottawa district. We thus 

 have in the crystallines, rocks produced in two different ways. 



Throughout the districts in which these rocks occur there 

 are often great masses of granite, anorthosite, diorite and 

 pyroxenic rocks, some of which also shew a gneissic structure ; 



