164 REPORT OP THE AMERICAN COMMITTEE. 
Arcliean ami perhaps of Carboniferous age, the latter, as it seems 
to me, in the vicinity of Boston)." 
Prof. M. E. Wadsworth would employ in American geol- 
ogy none of the terms mentioned. 
Capt. C. E. Dutton does not think that we can as yet identify- 
any American rocks as the equivalents of the so-called Hebrid- 
ian, Dimetian, Arvonian, and Pebidian, and, therefore, the use 
of such terms would be mere guesswork. 
Prof. Pumpelly : " Do not need them on this side of the 
Atlantic." 
Prof. A. Winchell is not aware of any recognized use of 
these terms, and does not know the petrographic or stratigraphic 
equivalence of Arvonian, which has been proposed to stand in 
the gap where he has placed Marquettian. 
It thus appears that all but two geologists who have expressed 
an opinion, are opposed to the use of these terras in American 
geology. One of these two thinks that American names should 
have priority, and the other would retain Arvonian for the for- 
mation immediately preceding the Huronian, and Hebridiau for 
Lower Laurentian. 
The opinion is about ten to one, so far as it has been expressed, 
against the use of any of these terms for our native measures. 
G. Are there crystalline rocks in and after the 
Paleozoic, lithologically indistinguishable from 
THOSE OF THE ArCHEAN ? 
It is a moot point among some of the foremost geologists in all 
countries whether a combination of structure and mineralogical 
constitution, in other words, qualities determinable by the eye, 
have, or ever will have a significance of the same kind as the re- 
mains which permit us to judge of the stages of life which existed 
in successive systems. .Some who deny the first part of the propo- 
sition admit the second. The question is not a new one, but 
one of those ever recurring. By the painstaking citations in the 
work of Profs. Whitney and Wadsworth, it is shown that almost 
every geologist who has written on the subject of the crystalline 
rocks, has at one time or another sought to correlate masses of 
