been realized in the eastern portion of the Adirondack area, where the limestone is thinnest. The main problem of the region, the origin of the gneisses, is as yet far from settlement. The tendency is, however, to ascribe to them an igneous origin, and to place them later than the Oswegatchie series, in the areas where they have been most closely studied.

Jones,' in connection with a description of Tallulah Gorge of northeastern Georgia, describes the crystalline rocks there occurring, and gives a little sketch map showing their relations. They are called pre-Cambrian.

Watson describes the granitic rocks of the Piedmont plateau of Georgia. Field and laboratory studies indicate that they are not all contemporaneous in origin. Some of them are pre-Cambrian, while others may possibly be later in age.

Adams describes the Laurentian granitoid gneiss and granite of the Admiralty group of the Thousand Islands, Ontario. The granitoid gneiss is presumably derived by metamorphism from the granite. large exposure of crystalline limestone on Island No. 18 resembles in all respects that of the Grenville series of the mainland adjacent.

Parks describes the geology of the Moose River Basin in Canada, including the Moose and Abitibi Rivers, tributary to James Bay. This is an immense triangular area of which the apex is at James Bay, and the base stretches from above Lake Abitibi to a point west of Kabinakagami. The southern and major portion of this triangular area consists of Laurentian gneisses and granites crossed, by bands of Huronian rocks. Along the Abitibi River, Huronian rocks, consisting of altered diorites, pyrites, gray quartz schists, and some soft decomposed schists occupy the country to the south, extending as far north. as the head of the first long rapid on the Frederick House River. The line of contact of this belt crosses the Abitibi below the Iroquois

'The Geology of the Tallulah Gorge, by S. P. JONES: American Geologist, Vol. XXVII, 1901, pp. 67-75.

2

The Granitic Rocks of Georgia and Their Relationships, by T. L. WATSON : American Geologist, Vol. XXVII, 1901, pp. 223-225.

3 Notes on the Geology of the Admiralty Group of the Thousand Islands, by FRANK D. ADAMS: Can. Rec. of Sci., Vol. VII, 1897, pp. 267–272.

4 PARKS, WILLIAM A.: The Nipissing-Algoma boundary, Eighth Rept. Ont. Bur. Mines, 1899, pp. 175-204, with geological map; Niven's base line, Ninth Rept. Ont. Bur. Mines, 1900, pp. 125-142; The Huronian of the Moose River Basin, University of Toronto Studies, Geol. Series No. 1, 1900, pp. 35, with sketch map.

Falls. From this point to the Lobstick portage, Laurentian gneisses and mica schists crop out occasionally. The narrow Huronian belt from the Lobstick to the foot of the canyon or Long Portage, consists mainly of augite-syenite, passing into gabbro to the north. Beyond this portage Laurentian gneiss extends to the Devonian contact above the Sextant rapids.

Coleman' gives a general account of a visit to all the iron and copper regions of the Lake Superior country. For the ranges on the United States side of the boundary no facts are given not found in the published reports. On the Canadian side of the boundary the Michipicoten Range, the iron formation near Dog River, and the siliceous iron ores of Batchawana Bay are described. In the Michipicoten range the Helen mine in particular is referred to. In general, the rocks, including the ore at this mine, have all the appearance of Lower Huronian or Keewatin rocks, as in the Vermilion district, and not those of the Upper Huronian or Animikie, as in the Mesaba.

Near Dog River are iron formation rocks similar to those extending northeast from Michipicoten bay. It is thought probable that the two may connect.

The occurrence and relations of iron formation material northeast from Michipicoten Bay and near Dog River are indicated on a sketch map.

Coleman, as a result of an examination of the new Michipicoten iron district, and the consideration of other iron formation areas in Ontario, has collected facts which seem to throw some light on the relative ages of the different areas mapped as Huronian on the north shore. In the Michipicoten district iron-formation material, consisting of banded ferruginous sandstones, cherts, and jaspers, standing nearly vertical, extends from Little Gros Cap northeastward for twenty miles; then bending to the north and west it takes a westerly direction for more than thirty miles. The width of the belt is but a few hundred yards.

Sandstones of the same peculiar type occur at Little Turtle Lake, east of Rainy Lake and near Fort Frances, on Rainy River, as well as at the Scramble gold mine, near Rat Portage, on Lake of the Woods.

'COLEMAN, DR. A. P.: Copper and Iron Regions of Ontario, by A. P. COLEMAN. Report of the Ontario Bureau of Mines for 1900, pp. 143-191.

2

Upper and Lower Huronian in Ontario, by ARTHUR P. COLEMAN : Bull. Geol. Soc. Am., Vol. II, 1900, pp. 107-114.

Thin sections of these rocks show the same polygonal shapes of the grains of quartz, and more or less iron ore is associated with specimens from each locality. It is very probable, then, that the same horizon exists at points far to the west of Lake Superior.

Turning toward the east, specimens very like the jaspery varieties of the Michipicoten iron range are found interbedded with iron ores near Lakes Wahnapitae and Temagami, between Sudbury and the Ottawa River.

At Batchawana Bay at the southeast end of Lake Superior, a siliceous rock with narrow bands of magnetite occurs, which is probably the equivalent of the Michipicoten rock.

If, as seems probable, these jaspers are the equivalents of the western Huronian sandstones, there is a definite horizon traceable from point to point across the whole northern end of the province, a distance of more than six hundred miles.

At a number of places over this area conglomerates, containing jasper, ferruginous sandstone or chert pebbles, probably derived from the source above described, are known. Beginning at the west, some of these conglomerates occur as follows: on Shoal Lake, east of Rainy Lake; west end of Schist Lake; near Mosher Bay, at the east end of Upper Manitou Lake; a mile east of Fort Frances on the Rainy River; near Rat Portage; near the mouth of Dorè River; in the original Huronian area, north of Lake Huron, particularly the Thessalon area; on Lake Temiscaming.

It is assumed that the iron-formation material cannot be other than Lower Huronian, and that the conglomerates must represent a basal horizon of the Upper Huronian. The break between the Upper and Lower Huronian thus represented is a most profound one, and affords a good basis for the correlation of the Huronian formations. It is further suggested that this great unconformity may be the same as that between the Upper and Lower Huronian formations on the south shore of Lake Superior and in Minnesota.

Comment. As stated by Dr. Coleman a number of the conglomerates above mentioned have been regarded by Pumpelly, Irving, Van Hise, and other United States geologists, as basal to the Lower Huronian --- on structural evidence. Dr. Coleman places them in the Upper Huronian because they contain fragments of iron formation material which are assumed to be Lower Huronian. According to the generally accepted ideas of the number and relations of the pre-Cambrian

iron bearing formations, this assumption is perfectly justified and the conclusion follows as to the Upper Huronian age of the typical conglomerates mentioned.

But, lately evidence has been accumulated pointing to a conclusion of a rather radical nature. This evidence has been such that Van Hise' in a general article on the iron bearing formations of the Lake Superior country just published, describes three iron bearing formations, the Upper Huronian, Lower Huronian, and Archean. The most important of the Archean iron bearing formations are the Vermilion and the Michipicoten.

Van Hise himself in his published articles on the pre-Cambrian has persistently maintained the essentially non-clastic nature of the Archean, and the post-Archean age of all the iron bearing formations of the Lake Superior country. But new evidence on the subject, secured principally during the past year, has been so decisive that he has not hesitated to announce as proven the existence of an Archean or Basement Complex iron-bearing formation.

If there is an Archean iron formation, to which the Michipicoten and Vermilion iron formations belong, then Dr. Coleman's argument as to the Upper Huronian age of conglomerates containing iron formation fragments is rendered ineffective, and the conclusions indicated by the structural evidence that the great conglomerates and accompanying rocks above described are Lower Huronian must stand, until decisive evidence to the contrary is found.

Grant describes and maps the Upper and Lower Keweenawan copper-bearing rocks of Douglas county, Wisconsin. The Lower Keweenawan appears in a broad belt running from northeast to southwest across the county, widening toward the southwest, and in a sinall belt cutting through the southeastern corner of the county. It consists mainly of basic lava flows, associated with which, in the area in the southeast corner of the county, are a few beds of conglomerate composed of débris of the closely adjacent underlying rocks. The Upper Keweenawan appears in a broad belt in the southeastern part of the county between the two belts of Lower Keweenawan rocks. It The iron-ore deposits of the Lake Superior region, by C. R. VAN HISE: Twenty-first Ann. Rept. U. S. Geol. Surv., Pt. III, 1901, p. 322.

Preliminary Report on Copper Bearing Rocks in Douglas county, Wisconsin, by U. S. GRANT: Wisconsin Geological and Natural History Survey, Vol. VI, 1900, pp.

55.

is a series of conglomerates, sandstones and shales. In a belt north of the northern belt of Lower Keweenawan rocks, extending from these rocks to the shore of Lake Superior, is the Lake Superior sandstone (Cambrian). This is either flat-lying or dips slightly toward Lake Superior. The junction of the sandstone with the Lower Keweenawan is marked by a fault, along which the Lake Superior sandstone has been depressed, in some places probably as much as several hundred feet.

The Upper and Lower Keweenawan belts form a syncline, the axis of which runs northeast and southwest through the center of the tract underlain by Upper Keweenawan rocks.

While the Keweenawan rocks of this area are the same in kind and age as are the productive copper-bearing rocks of Keweenaw Point, the probable unproductive character of the Douglas county rocks is intimated.

Alexander Winchell' prefaces a detailed petrographical description of certain phases of the gabbroid rocks of Minnesota with a brief account of the general succession in structure of formations in northeastern Minnesota. This is essentially the same as given by N. H. Winchell in Volumes IV and V of the Minnesota State Survey. The correlation of this succession with the succession determined by the United States Geological Survey is discussed.

Comment. Mr. Winchell's ideas as to succession and structure determined by the United States Geological Survey are naturally derived mainly from Bulletin 86 of the Survey and from the "Principles of Pre-Cambrian Geology" published in the Sixteenth Annual Report of the Survey. However, since these reports have been issued, the United States Geological Survey has done somewhat detailed field work in northeastern Minnesota as a result of which the ideas of the United States geologists on the succession and correlation have been considerably changed. The new conclusions of the Survey are briefly outlined by Van Hise in the Twenty-first Annual Report. This paper should be referred to by anyone reading Mr. Winchell's discussion of the correlation.

I Mineralogical and Petrographic study of the gabbroid rocks of Minnesota, and more particularly of the plagioclastites, by ALEXANDER N. WINCHELL: American Geologist, Volume XXVI, 1900, General part, pp. 153-162, with geological sketch map of Northeastern Minnesota.

See summaries, JOUR. GEOL., Vol. IX, pp. 79-86.