The Kciveenazvafi hi Minnesota. — Elftman, 103 
much larger than that of the present lake. Lake Duluth oc- 
cupied the greater part of region occupied by lake Nemadji. 
The prominent features of the lake are its clay deposits, 
beaches and deltas. 
Clay Deposits. These deposits are abundant in the entire 
area of lake Duluth. In the region southwest of Duluth the 
clay does not occur at an altitude over 1,050 feet above the 
sea. Along the north shore of lake Superior the highest alti- 
tude of the clay rises toward the northeast. This has been 
verified by numerous aneroid measurements. North of Silver 
mountain, Ontario, the clay is found at an altitude of 1,200 
feet above sea level. 
The clay is stratified and varies in thickness from a few 
inches to one hundred feet, forming locally,' flat areas of con- 
siderable extent. The most abundant deposits are found in 
the vicinity of the mouths of the larger glacial rivers. The 
clay is composed entirely of very fine grained particles. In 
the admirable sections through the clay along the Port Ar- 
thur, Duluth and Western railroad, from Port Arthur to Sil- 
ver mountain, and in the region southwest of Duluth, it is 
seen that the clay originally had a blue or gray color. The 
w^eathered surfaces always show a yellow to red color, and a 
gradation from the blue to the red is noticeable in many recent 
exposures. The depth of alteration varies considerably, ex- 
tending from five to twenty-five feet below the surface. Many 
streams have cut gorges through the deposit and have ex- 
posed the pre-lacustrine surface of glacial drift and the earlier 
rock formations. 
Beaches. Above the clay, and often cutting into it, are 
beaches which represent the stationary periods of the lake. 
These beaches are found in numerous localities, but on ac- 
count of the heavy timber it is impossible to follow them con- 
tinuously. The highest beach of lake Duluth is always found 
above the clay, and generally represents the highest lacustrine 
deposit. 
In the western end of the lake the altitudes of the glacial 
outlets and of the highest beaches, as they are at present re- 
corded, do not agree, unless we suppose an ascent of the 
beaches of three to four feet per mile toward the northeast. 
This does not seem warranted by observations in other parts 
