486 ADDRESS OF T. STERRY HUNT. 
given by me in 1869,* it may be added that the observations of 
Mr. Richardson, during that season, on the north side of the Gulf 
of St. Lawrence, confirm the previous conclusions, and show that 
the rocks of the Labradorian (or rather N orian) system there re- 
pose transgressively, and often at comparatively moderate angles, 
on the nearly vertical Laurentian gneisses.— We may, I think, in 
the present state of our knowledge, regard these norites or Norian 
rocks as portions of a pre-Huronian system. 
Ul. The Origin of Crystalline Rocks. 
We now approach the second part of our subject, namely, the 
genesis of the crystalline schists whose history we have just dis- 
cussed. The origin of the mineral silicates which make up a great 
portion of the crystalline rocks of the earth’s surface is a ques- 
tion of much geological interest, which has been to a great degree 
overlooked. The gneisses, mica-schists and argillites of various 
geological periods do not differ very greatly in chemical constitu- 
tion from modern mechanical sediments, and are now very gene- 
rally regarded as resulting from a molecular re-arrangement of 
similar sediments formed in earlier times by the disintegration 
of previously existing rocks not very unlike them in composition ; 
the oldest known formations being still composed of crystalline 
stratified deposits presumed to be of sedimentary origin. Before 
these the imagination conceives yet earlier rocks, until we reach 
the surface of unstratified material which the globe may be sup- 
posed to have presented before water had begun its work. It is 
not, however, my present plan to consider this far-off beginning of 
sedimentary rocks, which I have elsewhere discussed. ¢ 
Apart from the clay and sand-rocks just referred to, whose com- 
position may be said to be essential] y quart 1 alumi ilicates 
chiefly in the forms of feldspars and micas, or the results of their 
partial decomposition and disintegration, there is another class 
of crystalline silicated rocks which, though far less important in 
bulk than the last, is of great and varied interest to the litholo- 
gist, the mineralogist, the geologist and chemist. The rocks of 
this second class may be defined as consisting in great part of the 
silicates of the protoxyd bases, lime, magnesia and ferrous oxyd, 
*On Norites, etc., Amer. Jour. Sci., II, xlviii, 180, 
t Geol. Survey of Canada, Report 1866-69, p. 306. 
t Amer. Jour. Science, II, 1, 25, 
