98 C. H. GORDON— SYENITE-GNErSS (lEOPARD ROCK) FROM CANADA. 



gneisses and pyroxenic and feldspar rocks above the Gatineau limestone 

 band (III). 



As shown on the map, in the region between the Gatineau and Du 

 Lievre rivers the rocks are arranged in the form of a great synclinal, -with 

 Big lake marking approximately the location of the axis. On })assing 

 eastward from the west line of Ottawa county, therefore, we pass over 

 the different belts in ascending order until we reach the cast line of Den- 

 ham township. 



Lithological characters. — The gneisses interstratified with the limestones 

 vary much in character, but the predominating variety consists of a more 

 or less reddish orthoclase and grayish white quartz with little or no mica 

 and sometimes with garnets. It is usually coarse or granitoid in struc- 

 ture and the bedding often obscure, though in places it contains numer- 

 ous beds or layers of quartzite from half an inch to a foot in thickness, 

 which render the strike of the rock plainly visible. In some cases the 

 mica is abundant and the gneiss then assumes a marked foliated char- 

 acter. The micaceous gneisses are sometimes garnetiferous and occa- 

 sionally exhibit the texture of the so-called augen-gneiss. 



Quartzites of considerable thickness occur now and then. They are 

 often white and glassy and in places contain a little orthoclase. These 

 strata are frecjuently traversed by dolerite dikes, some of which are of 

 considerable thickness. 



The pyroxenic rocks associated with the apatite, and by Hunt* called 

 pyroxenites, vary considerably in their characters. Sometimes they con- 

 sist almost exclusively of pyroxene, though commonl}^ quartz and ortho- 

 clase are present. Mica and apatite are of frecpicnt occurrence, and 

 occasionally minute garnets may be seen. 



HI OH ROCK DISTRICT. 



General description. — High Rock mine, the locality at which the ma- 

 terial for this study was obtained, is located on a series of connected 

 hills situated on the right bank of the Du Lievre river, about 21 miles 

 above Buckingham. The openings cover in all about 600 acres on the 

 tops of the hills which extend to a height of 700 feet above the level of 

 the river. They are reached from the river by a tramway two miles long 

 following the natural slope of the hill. The series of hills trend in a direc- 

 tion south 30° east (magnetic). The openings are all in one wide belt of 

 pyroxenic rock having a strike in the same direction. The main opening 

 is number 11, the entrance to which is on the west side of the hill about 

 180 feet below the summit. The vein in which this pit is oi)ened has 

 been worked at several places along the side of the hill. Other veins 



♦ Geology of Canada, 18G6, p. 185. Chemical and Geological Essays, p. 208. 



