136 - T. Sterry Hunt on Granitic Rocks. 
in the second part of this paper, § 16—§ 23.* 
urentian series, the Lower Laurentian of Sir Wilham — 
Logan, as studied by him in a region to the north of the Ottawa, 
the only area in which it has yet been examined in detail, — 
appears to consist of an alternation of conformable gneissic and 
calcareous formations. The latter are three in number, each 
tain series, which, with their veinstones, have been treated of — 
occasionally with a white triclinic feldspar. They are often 
hornblendic, and sometimes contain small quantities of dark- 
colored mica. A white granitoid gneiss, composed chiefly of 
orthoclase and quartz, sometimes contains an abundance of 
iron-garnet. The latter mineral is often disseminated, or forms 
subordinate beds in the quartzites of the series. 
§ 33. With the crystalline limestones of the calcareous paris 
of the series are often found strata made up of other minerm® 
to the entire exclusion of carbonate of lime, by an admixture of 
which, however, they graduate into the adjacent limeston® 
These generally consist of pyroxene, sometimes neatly 
pure, and at other times mingled with a magnesian mica, 
with quartz and orthoclase, often associated with hornblende, 
serpentine, magnetite, sphene and graphite. These pyran 
rocks are generally i ture, 
sometimes very coarse-grained. They occasionally assume @ 
e limestones often include serpentine, pyroxene, hornblende, 
phlogopite, quartz, orthoclase, magnetite and graphite; 5° 
; 
* A good example of a large vein of this kind of intersecting rocks, , Ee 
™: i fi 
the city of New York. Its place is marked by a great erratic block perched 
- structure described in § 21 is well shown in a narrow 8" "0 Rock 
which I owe to Prof. Haughton of Trinity College, Dublin, got from ~_— some 
Mountain near that city. It consists of white orthoclase, with quartz amy 7 
mica and garnet, and exhibits near the middle two bands of prisms of lin 
see pointing towards the centre, which is filled with a coarsely : 
