American Geology, by T. S. Hunt. 395 
have to ohjent that the seaigeege gneiss is identical with the Green 
Mountain gneiss, not only in lithological character, but in the 
presence of certain rare Soon such as chr rome, titanium, and 
nickel which characterise its magnesian rocks; all of these we 
have shown to be present in the unaltered sediments of the Que- 
bee group, with which Sir William Logan has identified the 
gneiss formation in question. Besides liek the lithological and 
chemical vharacters of the Appalachian gneiss are so totally dis- 
tinct from the crystalline strata of the Laurentian system, with 
which Prof. Rogers would seem to identify them, that no one 
who has studied the two can for amoment confound them. Prof. 
Jogers is therefore obliged to assume a new ie os aoe 
rocks, distinct from both the Laurentian and Hur uae 
sys e elsewhere indicated the general principles 
upon which this ion of a progressive change in the composi- 
tion of sediments is b and shown how the gradual removal 
of alkalies from aluminous ake has led to the formation of ar- 
gillites, chloritic and epidotic rocks, at the same time removing 
carbonic acid from the atmosphere, ‘while the re resulting carbon- 
ate of soda by decomposing the calcareous and magnesian salts 
i Dr carbonates for the formation of lime- 
stones and dolomites, at the same time generating sea salt. 
Closely connected with these oan a is that of the 
commencement of life on the earth. The recognition beneath 
the Silurian and Paseisn rocks, of 40, 000 feet of sediments 
analogous to those of more recent times, carries far back into the 
ihe 2 sew He in 1824 described an extensive tract of Aatheso rocks on Rainy 
Lake and Lake Lacroix, north of Lake Superior. The general course of the strata 
he states to 5 “from N.W. to N. by W., witha oping!) Ne easterly died wm 
“ 1s 1SS 
‘oo mM: to Dr. Bisby 
vations on the geogn mate of ge. Potty A 
