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The Great Kankakee — the valley's first river, southwest-flowing, and the lake the literature sets in its channel
One valley, two watersheds: The second section of Howard's topography chapter gives the county's master fact in one sentence of Montgomery's: from an examination of the geological formations from Lake Huron and Saginaw Bay, following the valleys of the St. Joseph and the Kankakee, "those two great valleys were originally one; and that, at a remote period, the waters of Saginaw Bay flowed through southwestern Michigan and northwestern Indiana, reaching the Mississippi by way of the Illinois River. The broad flood plain marked out in geological ages, and through which flowed the mighty stream, called by Dr. Montgomery the Great Kankakee, may still be traced over the whole region from Saginaw Bay to the Mississippi, passing through the heart of St. Joseph county." The valley Mishawaka stands in was dug and floored by a river flowing the opposite way from the present one — southwest, to the Gulf of Mexico — before it ever carried water to Lake Michigan.
The channel at this ground: Montgomery's measures for the ancient waterway, as the county history prints them: where the city of South Bend now lies, "a wonderful river once flowed, a stream three miles wide and one hundred feet or more in depth, moving from east to west," fed from the north by a tributary — the glacial Dowagiac — whose mouth was likewise three miles wide; to the northeast, a flood "from five to six miles in width… passing at his feet and rolling onward to the southwest, confined only by the hills on the north and on the south." The flood plain of the old channel "varies in width from three miles at its narrowest point, which is one mile below South Bend, to about twenty at its broadest," with its southeasterly bank "from fifty to one hundred feet high." Five miles east and up the valley from South Bend — this city's reach — the valley "reaches a width of six miles, which width it holds, with slight variation, until it arrives at the rim of the Saginaw basin," and that upper reach "is thoroughly drained by the present St. Joseph river. There are a few peat bogs and marshes lying back from the river where the valley is broad… Otherwise the old valley above South Bend is one vast level sand-plain." The same breadth of sand plain, undrained, is what lay on Penn Township's south side, and the swamp entry below takes it up.
The rock that ponded it: The ancient river's width had a cause the survey could point to. Beyond the present Illinois line the stream "crossed the arched bed rock which extends in a northwesterly course across Indiana into Illinois. Near the present site of Momence, Illinois, this rocky ridge produced a well marked rapids, similar to that in the Ohio river near Louisville, which tended to dam the waters and cause them to overflow a wide territory above and causing this region to appear today as if a great lake had occupied the territory." The Momence ledge is the hinge of the whole valley system: the same limestone barrier that ponded the glacial river stands behind both the lake and the marsh of the later literature.
The lake form of the same water: The geological literature after Montgomery gives the ponding a lake's name and a lake's dates, and the two tellings are carried together here as the literature's two forms of one water. Glacial Lake Kankakee, in existence by about 14,000 years ago in the standard lake-history accounting, formed from the outwash of all three lobes ponded in the valley; in Edward Barrett's 1916 report for the state geological survey its northern waters stretched "to the marshes southwest of South Bend." About 13,000 years ago, in the same accounting, the lake drained down until it reached the level of the Momence limestone ledge, and unable to cut through it, shallowed into the Grand Kankakee Marsh — carried in the literature at 400,000 acres of wetland in the Fraser and Bleuer framework (1991) and 500,000 acres in the standard lake-history accounting. Montgomery's river with a lake-like ponded reach (1907) and Barrett's lake in a river's valley (1916) differ in form more than in substance; the dates of the lake form are the lake literature's, printed at their strength. Behind both stands the flood that scoured the valley: the Kankakee Torrent, named in Leverett's United States Geological Survey Monograph 38 (1899), and dated by the modern study of the deglaciation floods (Curry, Hajic, Clark and others, 2014) to about 19,000 years ago. The popular telling stands on a marker at South Bend — ice "perhaps a half a mile thick," the Glacial Kankakee "one mile wide and at least 100 feet deep" coursing through the present downtown — printed here at its size: a marker's figures, narrower than Montgomery's surveyed channel, on the neighboring city's ground.
Sources: Howard (1907), Chapter I, §§II and VII — Montgomery's one-valley conclusion, the three-mile channel, the flood-plain widths, the six-mile reach above South Bend, the Momence arched bedrock and its rapids; Barrett, 41st Annual Report, Indiana Department of Geology and Natural Resources (1916) — Lake Kankakee's northern waters, as carried in the South Bend leg of this project; Fraser & Bleuer (1991) and the standard lake-history accounting — the marsh acreage range, the lake's formation and draining dates at the Momence ledge, as carried in the South Bend leg; Leverett, USGS Monograph 38 (1899), and Curry, Hajic, Clark et al. (2014) — the torrent's naming and modern date; "A Window To Our Past," Indiana historical marker at South Bend, text as transcribed by the Historical Marker Database — the popular figures.