156 PLEISTOCENE OF INDIANA AND MICHIGAN. 



Nottawa Creek. Between Pine and Nottawa creeks, in the vicinity of the hamlet of Abscota, 

 the surface of the gravel plain is bowlder strewn for 1^ to 2 miles out from the moraine. 

 Between Nottawa Lake and St. Joseph River, basins (one of which contains Turtle Lake, with 

 an area of about one-half square mile) are conspicuous for 3 or 4 miles southwest from the 

 moraine. The plain has a rapid southwestward slope, its altitude next to the moraine being 

 about 975 feet, opposite Athens (8 or 10 miles southeast) 900 feet, and opposite Leonidas and 

 Colon (8 miles farther) about 860 feet. Beyond the last-named place it descends perhaps 2 

 feet per mile down the St. Joseph Valley to the head of the Kankakee at South Bend, its altitude 

 at that city being about 720 feet. The gravelly and cobbly part of the plain is chiefly in the 

 rapidly sloping part above Colon, the remainder being a sand or sandy gravel. 



In the St. Joseph plain are features that seem to indicate considerable filling or aggradation, 

 and also some cutting down, for the borders of the gravel plain all the way up to the Tekonsha 

 moraine are determined by distinct bluffs of till. The bluffs generally are only 15 to 30 feet 

 above neighboring parts of the gravel plain after due allowance has been made for trenching 

 of the gravel plain by modern streams. They are abrupt, as if cut down rapidly, and that, too, 

 in a valley which from Burlington down to Colon is fully 6 miles hi average width. Filling or 

 aggradation is shown by the character of the deposits, which throughout the valley and to 

 depths as far as the wells ordinarily penetrate (20 to 40 feet) are assorted water-laid material, 

 strikingly different from the material of the bluffs. 1 The basins also suggest a filling of the bor- 

 dering tracts, for they seem to be the result not of excavation by the glacial stream but of the 

 melting of stagnant ice masses that persisted until the valley aggradation was completed. 

 The most probable interpretation is that a very large valley, as broad as this gravel plain and 

 considerably deeper than the depth of the gravel plain below the neighboring till tracts, was 

 first excavated and afterward partly filled with the gravel and sand. It is a matter of obser- 

 vation that large streams like the Mississippi and Missouri rivers scour portions of their beds 

 at flood seasons to depths approaching 100 feet, and then at ordinary river stage slowly fill the 

 holes thus produced. The meanderings of current may hi the course of time bring all parts of 

 the valley under deep scouring action followed by partial filling, and thus give it the appearance 

 of having once been more deeply excavated. 



INTERMORAINIC GRAVEL PLAIN. 



Immediately above Burlington, where St. Joseph River emerges from the Tekonsha moraine, 

 the valley is a scant hah mile in width and contrasts strikingly with the broad gravel plain 6 

 to 9 miles wide which the river enters immediately outside the moraine. Nevertheless, glacial 

 drainage prevailed through this narrow part of the valley during the recession of the ice, for 

 it served as the outlet from a gravel plain that lies within the moraine just north of Tekonsha. 

 This latter plain covers about 12 square miles and stands a few feet lower than that outside 

 the moraine, its altitude at Tekonsha station being 945 feet. To escape westward down the 

 St. Joseph Valley it must have trenched the headward end of the large plain outside the moraine 

 to a depth of 30 feet or more. This inner plain seems to have a slight slope southward from the 

 inner part of the moraine at Nonosseppe Lake to the St. Joseph Valley at Tekonsha. Its mate- 

 rial is a rather fine gravel, in places sandy. 



GRAVEL PLAIN OF HOG CREEK. 



On the outer border of the moraine immediately south of St. Joseph River a space of a mile 

 or more carries very little outwash. Beyond this space a gravel plain extends southward past 

 Hog Creek to the Coldwater Valley at Hodunk. It embraces what is known as Girard Prairie 

 and covers an area of about 15 square miles. The plain has an altitude of 990 to 1,000 feet next 

 to the moraine but slopes down to about 950 feet at the Coldwater Valley by Hodunk, a descent 



1 A boring on the Fimple farm, in sec. 20, Sherwood Township, and another on the Greenfield farm, in sec. 4, Sherwood, are each on this gravel 

 plain and are reported to have penetrated a great depth of blue clay, presumably till, under the gravel. In the Fimple boring the gravel is 30 feet 

 thick and the underlying blue clay was penetrated to a depth of 214 feet from surface without reaching the bottom. The Greenfield well is reported 

 to be similar. These notes were furnished by C. E. Swain, of Sherwood, Mich. 



