170 REPORT OF THE AMERICAN COMMITTEE. 
Prof. Pumpelly: " la the present state of our knowledge, I 
should say only locally." 
Prof. A. Winchell: "Generally, no; but a few minerals 
are restricted to particular ages." 
In reviewing these replies, it will be observed that while all 
are guarded and qualified, they evince a stronger tendency towards 
the main proposition than many recent writings would seem to 
indicate. Dr. Hunt asserts the general principle pure and sim- 
ple. Sir William Dawson, Prof. Irving, and Capt. Dut- 
TON claim it for the Lower and Middle Laurentian rocks, and 
the former also "locally" (which is often an embryo generally) 
elsewhere. Profs. Le Conte and Hitchcock think that one 
day it may be established, though it has not yet been. Dr. 
Emmons restricts it to relative age, which presumes a value of 
mineral constitution in determining age, though a restricted one. 
Prof. N. H. Winchell admits it of the rocks of Minnesota, 
and it is fair to presume that, with equal facilities for observation 
and the necessary time, this area might be indefinitely extended. 
Prof. Emerson admits it of limited areas, and Prof. A. Win- 
chell of certain rocks in which occur a few specified minerals. 
Even Prof. Dana, who has been regarded as the chief opponent of 
the unqualified statement that minerals were the fossils of crystal- 
line rocks, seems clearly to go as far as Dawson, Irving, and Dut- 
ton, for, in a letter on another matter to your Reporter, he says : 
" My work has, I believe, proved that the lithological canon is a 
most unsafe guide to true stratigraphical or chronological dis- 
tinctions. Still, you see in my paper,^ that I recognize some 
rocks as iu all probability exclusively Archean, such as chondro- 
ditic rocks, those containing Zircon abundantly. Zircon syenite, 
and related rocks of gneissic structure, and rocks containing 
scapolite, some kinds of augitic rocks. Yet I think the conclu- 
sion should have the proviso over it ' until proved erroneous.' 
The occurrence of chondrodite in Vesuvian throat-clearings is 
nothing against it, because the throat of the volcano may descend 
to an Archean chondroditic limestone, and the materials may be 
derived thence for the new crystallization. On the other hand, 
gneiss and other schists are among Archean rocks, as they may 
* Taconic Eocks and Stratigraphy, with a geological raap of the Taconic 
Regions, by Jas. D. Dana, Am, Jour. Sci. for April, 1887, p. 270, and May, 1887 
p. 393. 
