the archean. 167 
Peofs. Dana, Le Conte, Hitchcock, Wadsworth, Emer- 
son, Sir William Dawson, Dr. Emmons and Prof, A. 
Winchell think there are crystalline rocks in the Paleozoic and 
later which they cannot distinguish from some in the Archean. 
Dr. Hunt, Prof. N. H. Winchell, and Capt. C. E. 
Dutton believe that, broadly speaking, there are none when 
carefully studied, and Prof Irving inclines to this belief without 
dogmatically asserting it. 
There is no such unanimity of belief here as would warrant 
the statement of either view as that representing American 
opinion. 
H. Are there any crystalline rocks in the Archean 
WHICH DO not occur LATER? 
This question is complementary of the last. 
Prof. J. D. Dana says: " Chondroditic limestone is, I now 
think, of Archean only, except what is eruptive, and others are 
also distinctive, but not gneiss or mica-schist." 
Sir J. W. Dawson remarks : " Some varieties of orthoclase 
gneiss I have not seen in any later formation." 
Dr. Hunt : " The indigenous rocks of the Archean are not 
repeated later." 
Prop. Le Conte does not believe we can pronounce with cer- 
tainty, though often with probability. 
Prof. Irving includes this question with the last. The true 
banded gneiss of the Archean is simulated, not repeated. 
Dr. S. F. Emmons thinks, that while the Archean rocks, as a 
whole, are distinct from those of later formations, he would not 
venture to say that individual representatives of any of these 
varieties may not be locally developed in later formations. 
Prof. Hitchcock is of the opinion that we probably do not 
have the hyjiersthene, labradorite, olivine, and corundum associa- 
tions outside of the Laurentian in any large amount. Other 
minerals, also, are confined to the Laurentian. 
Prof. Wadsworth knows of no crystalline rocks in the 
Archean which do not occur later. 
Prof. Emerson thinks " there is rather a difference of habit, 
e.g., extremely coarse and perfect crystallization." 
Capt. Dutton answers this question, together with the last, 
