RR. D. Irving—Hornblende of the Northwestern States. 133 
occasionally notices’ the occurrence of augite in the green- 
Stones, he still regards them as mainly diorites, even speaking 
of one case from the Menominee region as the only instance 
of diabase in the Huronian then known to him,” Of the 
others who give descriptions of the Marquette and Menominee 
rocks in this volume Alport, Hawes, Julien, Rutley and Torne-. 
bohm, the last named only, so far as I have found, describes 
any of the secondary hornblende; but the exception is an 
important one, since he says of the hornblendic rock of Light 
House Point that it is ‘no true diorite, since it contains re- 
Mains of augite.”” The others, however, confirm Wichmann 
mm saying that diabase is widely represented in the Marquette 
and Menominee Huronian," and Hawes says that to judge from 
the sections some of the diabases are eruptive.” Brooks also 
Says of the greenstones of these regions that the hornblendic — 
and augitic varieties “ appear to graduate into each other, but 
whether through alteration or original differences in composi- 
tion, cannot always be ascertained.” ” 
Three months after the publication of the third eee of 
F é : 
In these he gives the general results of the examination of a 
large number of thin sections. So far as the. Copper Series is 
the pebbles of the Keweenawan conglomerates,—which had 
before been described macroscopically only, though correctly, 
by Pumpelly and Marvine—in which shows the frequent 
presence of the peculiar “quartz de corrosion’ descri Vy 
that many of the hornblendic Huronian greenstones, as pre- 
Viously shown by Pumpelly and myself for the hornblendie : 
weenawan greenstones of Northern Wisconsin, are but — 
oP 251. %p.691. %p,567, pp. 533-599. Meg, p. 570. 
- P- 519, 1 Bulletin of the Mus. Comp. Zool., vii. : 
