158 EEPORT OF THE AMERICAN COMMITTEE. 
Dr, Selwyn, Dr. Emmons, Prof. C. H. Hitchcock, and 
Mr. Thomas Macfarlane are not able to specify any non- 
conlbrmabilities. Prof. Hitchcock adds that he has only the 
New England rocks in mind. 
Prof. N. H. Winchell writes : 
" As Dana at first defined the Archean, there is a perceptible 
unconformity at the base of the Huronian, as I published in 
1880. (See my Ninth and Tenth Annual Reports, Minnesota 
Survey.) But as it is limited by Irving and others, making it 
embrace only Laurentian, I do not knOw of any unconformity in 
it, though I presume local unconformities have existed, which now 
are hid by folding and metamorphism. The unconformity 
between the Huronian and the Laurentian of Dana's scheme, I 
have fully verified in the past season. (See my brother's paper 
in the American Geologist, No. 1, vol. i.)" 
Mr. C. D. Walcott applies the word ' Archean ' of the ques- 
tion to the Laurentian, and says "as above defined it cannot be 
divided." 
Prof. Pumpet.ly has positiS^e personal knowledge of non- 
conformability between the Laurentian and the " Agnotozoic" at 
the base of the Keweenawan. 
Prof. A. Winchell says : 
" 1. Between Laurentian and Marquettian, there occurs a 
change in mode of geognostic action. The former rocks are 
crystalline, the latter normally uncrystalline. 
"2. Between Marquettian and Huronian, a stratigraphic un- 
conformability of a decided character." 
*Prof. Dana, Major Powell, Prof. Geo. H. Williams, 
Prof. B. K. Emerson, Capt. C. E. Dutton, and Prof. Blake 
do not state their views. 
There seems to be a belief, on the part of a large majority of 
those who have expressed themselves on the subject, that the 
Pre-Cambrian rocks consist of at least two systems, but they are 
unwilling at present to concede any but local planes of non-con- 
formability. There seems to be, however, an unexpressed belief, 
that at least one such plane — at the top of the Laurentian — is 
destined to be established by future work. 
* Prof. A. Winchell here apparently includes Dr. Hunt's Arvonian, but not 
with a like definition. 
