436 Wisconsin Academy of Sciences , Arts and Letters. 
culable as it is, might have been still greater but for the fact that all 
his material passed into the hands of his co-laborer, Professor Van Hise, 
who is intimately familiar with his unwritten as well as written views. 
Some of Doctor Irving’s leading conclusions from his later studies 
were set forth in his presidential address before the Wisconsin Acad¬ 
emy of Sciences, Arts and Letters, entitled “ Divisibility of the Aarchoean 
in the Northwest,” * * and more especially in the following very notable 
papers: “Preliminary Paper on an Investigation of the Archaean For¬ 
mations of the Northwestern States,”! “On the Classification of the 
Early Cambrian and Pre-Cambrian Formations. A Brief Discussion of 
Principles; Illustrated by examples drawn mainly from the Lake Su¬ 
perior Region,” J “ Origin of Ferruginous Schists and Iron Ores of the 
Lake Superior Region,” || “Is there a Huronian Group? ”^[ and the 
introduction to Bulletin Number 62 of the U. S. Geological Survey, 
“ On the Greenstones of the Menominee and Marquette Regions,” by 
Dr. G. H. Williams. 
During these later years in which he was chiefly engaged upon mono¬ 
graphic studies, he published numerous special papers, among which 
the more important were, “ On the Nature of the Induration of the St. 
Peter’s and Potsdam Sandstones, and of certain Archeean Quartzites in 
Wisconsin,”* “Paramorphic Origin of the Hornblende of the North¬ 
western States,” t “ On Secondary Enlargements of Mineral Fragments 
in Certain Rocks v J (jointly with Professor C. R. Van Hise), and “ The 
Junction Between the Eastern Sandstone and the Keweenawan Series 
on Keweenaw Point ” § (jointly with President Chamberlin). 
Professor Irving’s greatest contributions to science lay in the depart¬ 
ment of structural geology and genetic petrography. His investiga¬ 
tions upon the great copper and iron-bearing series and the adjacent 
formations of the Lake Superior region, constitute a contribution of 
the first order. The deep sympathy of the present writer with Pro¬ 
fessor Irving’s views on questions that have been subjects of divergence 
of opinion should perhaps restrain him from a full expression of his 
appreciation of the profound value of this work, lest a color of personal 
partiality be thrown over this sketch, but it is not too much to assert 
that supporter and opponent alike recognize the ability which has char¬ 
acterized these investigations, and the high order of value which must 
attach to them whatever interpretations may finally prevail. 
* Am. Jour. Sci., Vol. XXIX, pp. 237-249, 1885. 
t U. S. Geol. Survey, Fifth Annual Report, pp. 181-241, 1885. 
$ U. S. Geol. Survey, Seventh Annual Report, 1886. 
|| Am. Jour. Sci., Vol. XXXII, p. 255, 1886. 
1 Am. Jour. Sci., Vol. XXXIV, pp. 204-249, 1887. 
* Am. Jour. Sci., Vol. XXV, p. 401, 1883. 
*t Am. Jour. Sci., Vol. XXVI, p. 321, 1883. 
i U. S. Geol. Survey, Bulletin No. 8. 
§ U. S. Geol. Survey, Bulletin No. 23. 
