Reviews— Warren Upham on Lake Agassiz. 427 
The beautiful and evidently correct drawings in the numerous 
plates of this work have not been surpassed by any figures of 
similar fossils, and, with the careful work of Magister Fr. Schmidt, 
will go far to elucidate the nature, structure, and alliances of the 
Leperditian Ostracods, and the Peecilopodous, low Crustaceans 
occurring in a fossil state, especially in the Upper-Silurian strata. 
I{i.—Laxe Agassiz: a Cuaprer 1n Guactat Grorocy. By Warren 
Upnam. 8vo. pp. 26, and Map. (From Bulletin Minn. Acad. 
Nat. Sci., vol. ii.; printed in advance from 11th Annual Report 
of the Geol. and Nat. Hist. Survey of Minnesota, under the 
direction of Prof. N. H. Winchell.) 
ee years ago' Mr. Upham announced the discovery of un- 
mistakeable traces of a great Quaternary lake, in what is now 
the Red River Valley of Minnesota, Dakota, and contiguous British 
territory, and proposed for it the name of the chief founder of the 
glacial theory. The results of subsequent explorations, which have 
not only confirmed the suggestions of the preliminary reconnaissance, 
but developed many interesting subordinate features, are recorded in 
the present memoir. 
The lowest point in the Mississippi-Red River divide occurs in 
the west line of Minnesota, in a steep-sided valley 1 to 2 miles 
wide, and 125 to 150 feet deep, occupied in part by Big Stone and 
Traverse Lakes. From this point three distinct beach-terraces, at 
heights above the valley-bottom of 5, 55, and 85 feet respectively, 
extend north-eastwardly, forming the eastern margin of the far- 
famed Red River Valley. These beaches have been thoroughly 
explored and mapped, and level-lines have been carried along their 
crests for 175 miles, where they enter the impenetrable swamp- 
forests of Northern Minnesota. Throughout this distance the 
beaches (particularly the highest) are quite conspicuous, and practi- 
cally continuous and unbroken. When projected beyond the region 
thus explored, by means of known altitudes and recorded observa- 
tions of analogous beaches at various points in British America, 
these lines are found to include an area of greater length and 
little less width than Lake Superior. While these terraces are as 
manifestly wave-built as are those about the lakes to-day, Mr. 
Upham’s carefully measured level-lines have disclosed the significant 
fact that the beaches are neither horizontal nor parallel: all slope 
southward, and in a degree increasing from the lowest to the 
highest, and the inclination of all progressively increases from south 
to north; the absolute inclination of the uppermost in the 175 miles 
(or 142 miles measured on the meridian) being 125 feet, and its 
slope increasing from °4 ft. per mile at the south to ‘75, and finally 
1-5 ft. per mile at its northern extremity. Medially, the Red River 
Valley deposits are fine, clayey silts, horizontally stratified; but 
peripherally these pass into unstratified Boulder-clay, wave-washed 
superficially, but otherwise identical with that without the shore- 
lines. 
1 See Gzotocican Macazinez, Dec. II. Vol. VIII. 1881, p. 280. 
