CERTAIN PECULIAR ESKERS AND ESKER LAKES

OF NORTHEASTERN INDIANA

NORTHEASTERN Indiana is traversed by a series of massive moraines of late Wisconsin age, the joint product of the Erie and Saginaw lobes of the Laurentide ice-sheet. The Erie ice invaded the region from the south of east, the Saginaw ice from the east of north. Thus the general directions of ice movement in the two were at right angles to each other. The Saginaw lobe was relatively feeble and withdrew from the region before the Erie lobe. Along their line of contact there is much confusion, but it is possible to correlate the moraines and to mark out with considerable accuracy the limits of Erie and Saginaw drift.' The region abounds in unusual features. Half-filled valleys and abnormal drainage lines, isolated knobs and morainic outliers, clusters and chains of lakes, kettles, and kames conspire with esker-like ridges to produce a type of topography and scenery which seems artificial and almost bizarre. The southwestern portion of Noble county presents forms which are, perhaps, best described under the name of eskers.2

On the line between the townships of Noble and Washington a system of ridges occupies about two square miles and surrounds the basin of High Lake. The most prominent member is a gravel ridge one mile long, extending east and west along the south side of High Lake. It is highest and broadest at the east end, where it surrounds and encloses an oval kettle whose bottom is at lake level. The sides of the kettle rise to 25 and 35 feet at the lowest points, and to 70 and 85 feet at the highest points, which are at the ends of the oval. The westward extension of the ridge has a height varying mostly between 50

2

'Eighteenth Report Indiana Geology, pp. 28, 84.

The data for the maps, Figs. 1 and 2, were obtained with an aneroid and tape line, township, section, and farm lines, and the surface of the principal lake in each being used as bases.

and 75 feet, falling to 30 feet at one point where a ditch has been cut through it. The crest is usually sharp, and the lateral slopes are as steep as the material will permit. A small pit which has been opened on the southeast slope shows coarse rounded gravel without definite stratification. The ditch is cut through sand and fine gravel. At one point near the lake shore there is an outcrop of cemented gravel. These are the only exposures, and since the whole ridge is covered by a heavy growth of oak timber, investigation is difficult.

A mile and a half to the north the gravel ridge just described. is paralleled by an equally massive ridge of till which rises 50 to 60 feet above lake level and 30 to 40 feet above the general level of the country. It is broad and flat-topped with steep and symmetrical slopes, and pitted with numerous small kettles. It extends westward three fourths of a mile and then, bending sharply to the west of south, is prolonged an equal distance in that direction to the northwest corner of High Lake. The southern half of this portion, however, is composed of gravel; the transition from till to gravel being abrupt and marked only by a slight change in the trend. The gap between the ends of the two gravel ridges above described is almost closed by a series of broken ridges of sand, generally less than ten feet high, but rising in one sharp peak to forty feet.

From the central mass of the till-ridge two short spurs project toward the south. One of these is separated by only a small gap from a ridge of sand which continues in the same direction to the northeast corner of High Lake and along its eastern border. On the north it is broad, rounded, and 40 feet. high, but narrows and falls toward the south to a height of 5 feet, then widens and rises to 35 feet at the southern end. The lowest part of this ridge is a pile of angular bowlders up to a foot in diameter, with the interstices filled with sand.

The till-ridge is prolonged a mile or more to the northeast by a broad elevation of complex structure and topography. The greater portion of its mass seems to be composed of sand, which forms the highest peaks, 65 and 70 feet above lake level. An

area of at least twenty-five acres is studded with mounds and kettles, averaging about one each to the acre. One of these mounds has been excavated, and is shown to be made up of a uniform mixture of two thirds coarse gravel and one third clay. The clay forms a tough cement which holds up the material in a perpendicular face. The mixture might be called a clay conglomerate. A few large boulders occur in this tract. It is continued on the east by an isolated gravel mound rising to 65 feet above lake level.

The system of ridges forms an irregular parallelogram which nearly encloses the basin of High Lake. The northern part of the basin is occupied by a tamarack swamp. The area of open water is about half a square mile, mostly from 10 to 35 feet deep. It is deepest toward the south and west shores. There are no inlets except ditches from a few insignificant marshes, and in summer evaporation equals or exceeds supply. The overflow is by a small ditch to Bear Lake. The basins of the two lakes are really continuous, being only partially separated by the sand and boulder ridge. That their waters were once united is shown by a well-developed beach which borders the ridge and fills the gap between it and the till-spur.

This peculiar grouping of diverse and strongly marked features forms a puzzle difficult of solution. The east-west gravel ridge presents the characters of a subglacial esker, yet its height, steepness of slope, short extent and isolation are unusal. The presence of the great kettle hole piercing its center from top to bottom is not the least remarkable feature and contributes to the general impression of unnaturalness. The north-south ridges are sufficiently esker-like, but the western one is continuous, without notable change in form or direction, with the till ridge. The latter is an esker in form but its material is that of a submarginal moraine. Its northeastward extension presents some of the characters of a pitted sand plain or esker-delta, but it is complicated by the presence of the clay conglomerate and the kame-like sand and gravel knobs. The general indications of the surrounding country are that the Saginaw ice here moved