66 Adams— Contribution to our knowledge of the Laurentian. 
garnetiferous quartzite, the whole lying nearly flat and form- 
ing a southerly continuation of the series of horizontally 
banded gneisses shown in the accompanying photograph. 
II. Gneiss from the west shore of Trembling Lake, Province of 
Quebec. A fine grained dark gray gneiss composed of quartz 
and orthoclase with much biotite and containing numerous 
little white streaks which were evidently at one time con- 
tinuous little bands. These are composed of sillimanite. 
Garnets appear here and there in the darker portion of the 
rock. It occurs near a band of crystalline limestone which 
occupies the bed of Trembling Lake. | 
III. An ordinary roofing slate from Wales. Analyzed by T. 
Sterry Hunt. (Phil. Mag., 1854, 237.) 
IV. A similar roofing slate of Cambrian age, from the large 
quarries in the township of Melbourne, in the southern por- 
tion of the Province of Quebec. Analyzed by T. Sterry 
Hunt. (Geology of Canada, 1863, p. 600.) 
V. Gneiss from Darwin’s Falls near the village of Rawdon, Range 
V of the township of Rawdon, Province of Quebec. It isa 
highly quartzose garnetiferous gneiss and occurs in well 
defined bands interstratified with white quartzite, which is 
also often highly garnetiferous, the bands being from a few 
inches to several feet in thickness. 
VI. Red slate from near Tinzen in the district north of the Enga- 
dine, Switzerland. Highly siliceous, containing 9°12 per 
cent of silica as quartz. (Vom Rath, Z. d. G. G., 1857, 242.) 
VII. Gneiss, Lot 20, Range VII of the township of Rawdon. 
Gneiss composed essentially of malacolite, scapolite and 
orthoclase and holding a considerable amount of graphite 
and of pyrite. Weathers very rusty. Occurs in well 
defined bands interstratified with a grayish weathering gar- 
netiferous gneiss. 
The four gneisses I, II, V and VII, show no eataclastic 
structure, but when examined with a microscope seem to have 
undergone complete recrystallization under the pressure to 
which they have been subjected, no signs of crushing being 
now visible in the thin sections. 
The analyses show that the first three of these gneisses have 
the composition of slates. Nos. I and II have the composition 
of ordinary rooting slate, as will be seen by comparing these 
analyses with analyses III and IV and are quite different in 
composition from any igneous rock. The high content in 
alumina, the low percentage of alkalies and the great pre- 
ponderance of magnesia over lime, above mentioned as charac- 
teristic of slates will be noted. , 
No. V is a gneiss which is so highly quartzose that it might 
almost be termed an impure quartzite and also has a composi- 
tion differing from that of any igneous rock, but one which 
