4 Roland Duer Irclng — Chamherlin. 
work.§ This was the first approach to a unified and systematic 
discussion of this great formation occupying a tract of 40,000 
square miles and embracing portions of Michigan, Wisconsin, 
Minnesota and Canada. Whatever differences of opinion may 
continue to exist concerning the interpretation of the debated 
phenomena, this must ever be recognized as a monument of in- 
dustrious and able investigation and of candid and careful induc- 
tion. Following these studies upon the copper-bearing series^ 
professor Irving took up in a correspondingly comprehensive 
manner the investigation of the iron-bearing formations of the 
lake Superior region and their correlation with each other and 
with the original Huronian of Canada. Upon this work he was 
engaged at the time of his death. He had in preparation and 
nearing completion a monograph upon the Penokee-Gogebie 
range and had well in hand a large amount of material relating 
to the Marquette, Menominee and Vermilion lake series, as 
well as the original Huronian and Auimike groups. His loss 
at this fruitful stage of his work, incalculable 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 Dr. Irving's leading conclusions from his later 
studies were set forth in his presidential address before the 
Wisconsin Academy of Science Arts and Letters, entitled 
"Divisibility of the Archaean in the North-west,"* and more 
especially in the following very notable papers: "Preliminary 
Paper on an Investigation of the Archaean Formations of the 
North-western States,"t ''O^i the Classification of the Early 
Cambrian and Pre-Cambrian Formations. A Brief Dissussion 
of Principles; Hlustrated by examples drawn mainly from the 
Lake Superior Region, "| "Origin of Ferruginous Schists and 
Iron Ores of the Lake Superior Region," H "Is there a Huronian 
Group ?"1[ and the introduction to a forthcoming Bulletin o£ 
§"Copper- Bearing Rocks of Lake Superior." • Monograph V., U. S. Geol. 
Survey, 1883. 
*Am. Jour. Sci., vol. xkix, pp. 237-349, 1885. 
tU. S. Geol. Survey, Fifth Annual Report, pp. 181-241, 1885. 
JU. S. Geol. Survey, Seventh Annual Report, 1886. 
II Am. Jour. Sci., vol. xxxii, p. 255, 1886. 
^Am. Jour. Sci., vol. xxxiv, pp. 204-249, 1887. 
