24 



composed of rocks belonging to the newer systems. The rounded out- 

 lines of the hills are i-emarkably well seen from the Village of Chicoutimi, 

 on the River Saguenay, looking toward the north, and also, though in 

 a less marked mannei', from Parliament Hill, if one looks across the 

 Ottawa, over the Townships of Eardly and Hull, which, together with 

 the neighbouring Townships of Wakefield, Templeton, Portland, etc., 

 are composed almost exclusvely of these Laurentian rocks, affoi'ding us 

 here in Ottawa abundant material for their study. 



The most impoi-tant and by far the most common of the rocks 

 composing the Laurentian System is that which is known by the name 

 of gneiss. This term originated v,'ith the Fi'eiberg miners, who from 

 ancient times used it to designate the rock in which the veins of 

 silver ore occur, and more especially such parts of the rock as were 

 much decomposed. As now employed it denotes a foliated rock com- 

 posed of quartz, and orthoclase feldspar, which later, however, is 

 sometimes replaced in part by plagioclase feldspar. Hornblende, 

 pyroxene, mica and garnet are also common constituents, and in many 

 casesforma considerable proportion of the rock. Theso-called fundamental 

 gneiss of the north-west of Scotland, for instance, is, according to Zirkel, 

 principally hornblende gneiss, that is to say, contains hornblende in 

 addition to quartz and orthoclase, and^ as in the case of 

 the corresponding member of the family of the granites, this 

 variety, rich in hornblende, contains sphene, a mineral often found 

 abundantly in our apatite openings. Gneiss, like many of the eruptive 

 rocks, is seen, when thin sections are examined by means of the 

 microscope, to contain very numerous minute acicular crystals of apatite; 

 little zircon crystals and little particles of iron ore are also \erj com- 

 mon, and these three minerals, as a rule, possess much better crystalline 

 forms than the other constituents of the rock. The rock, as before 

 stated, is foliated, that is, the constituents are arranged in more or less 

 parallel bands. In these bands one mineral preponderates, but does 

 not, as a general rule, prevail to the total exclusion of the others. When 

 mica is present the leaves are arranged parallel to one another, thus 

 giving the rock a more or less easy cleavage along this plane. Gneiss 



* Diemikroskopische Beschaffenheit der Mineralien and Gesteine, p. 465. 



