THE ARCHEAN. 181 
In another letter, he says: "Serpentine is always an alteration- 
product of eruptive or sedimentary material, as the case may be." 
Peof. Geo. H.Williams: "Serpentine originates from the 
change of many eruptive rocks — generally Peridotites — and it is 
generally possible by microscopic study to ascertain the original 
rock. I know of no certain proof that Serpentine originates from 
sedimentary or chemically precipitated rocks, but I see no reason 
why it may not do so." 
Prof. Hitchcock ; " * * I am undecided, with a leaning to 
the view of Serpentine being an altered eruptive." 
Prof. N. H. Winchell: "So far as I know, Serpentine is 
always an alteration product from other eruptives." 
Prof. Wadsworth: "Serpentine is, when not a veinstone, 
an altered condition of Peridotite." [See reply to M. — Rep.] 
Prof. Emerson: "Serpentine is an alteration-product either 
of eruptive or sedimentary rocks." 
Capt. Dutton: "Certainly sometimes an alteration-product 
of Peridotite, and possibly of other rocks." [See answer to ^E. 
—Rep.] 
Prof. Pumpelly : " Always an alteration -product." 
Prof. A. Winchell : " So far as my observation goes, Ser- 
pentine is always an alteration-product of sedimentary rocks." 
Fourteen replies were received to this question. All but one 
regard Serpentine as an altered or after product, to wit : Dana, 
Dawson, Le Conte, Irving, Emmons, G. II. Williams, 
Hitchcock (doubtfully), N. H. Winchell, Wadsworth, 
Emerson, Dutton, Pumpelly and A. Winchell. 
Alone Dr. Hunt claims Serpentine as an original but not an 
eruptive rock. 
The view of the majority also here may safely be taken as ex- 
pressing the general opinion of American geologists. 
Conclusions. 
In summing up the conclusions drawn from the preceding 
work and attempting in them to summarize the drift of opinion 
of American geologists, it may be well to divide them into tiiose 
which relate to questions concerning the general groundwork of 
the nomenclature and color scheme, and those appertaining pecu- 
liarly to the Archean. 
