PRE-WISCONSIN DEIFT AND ASSOCIATED DEPOSITS. 65 



in the light of glacial movements and concluded that they may have all been transported by 

 the Labrador ice field from the vicinity of the south end of Hudson Lay or from the district 

 between Hudson Bay and Lake Superior, from which there is clear evidence of movement 

 toward the southwest and south to the localities where the diamonds have been found. But 

 though the movements of the Labrador ice field at both the Wisconsin and the Illinoian inva- 

 sions would favor such a derivation for the diamonds, or at least for those found between the 

 Wisconsin driftless area and Cincinnati, it should be remembered that like the copper they may 

 also have been transported by ice from the Lake Superior region, if that ice extended south- 

 eastward through the uj>per Great Lakes basins into Indiana and Ohio prior to the extension 

 of the Labrador ice field into the same region. Such a movement may have brought them 

 from the Patrician ice field recently described by Tyrrell. 1 (See p. 24.) It is necessarily diffi- 

 cult to work out the movements of such an ice sheet in territory where its deposits were sub- 

 sequently overridden and concealed by the drift of the Labrador ice, yet such an earlier move- 

 ment may contain the key to the home of the diamonds. If the lower of the two old drift 

 sheets of Indiana and Illinois pertains to the movement from the Superior region and only the 

 upper one to the Labrador field, the great extent of the diamond-bearing drift from northwest 

 to southeast may indicate the course of transportation of the diamonds instead of the terminal 

 line to which they were transported, and their home may be north of Lake Superior rather than 

 northeast of it. 



TOPOGRAPHY. 



The contrasts in topography displayed by the pre- Wisconsin drif t are fully as great as those 

 displayed by the Wisconsin drift. Indeed, the pre- Wisconsin includes some of the sharpest 

 drift ridges of the State and some of the smoothest plains. The ridges and knolls of this older 

 drift are less systematically distributed and are less definitely confined to moraines or otherwise 

 connected with the ice border than those in the newer drift. However, as far north as southern 

 Michigan, pre- Wisconsin ridges of morainic type are distributed in belts concentric with the 

 great basins. 



The flat surface of the greater part of the pre- Wisconsin drift, not only in Indiana but also 

 in Ohio and Illinois, seems to indicate that the retreating ice border did not make prolonged halts 

 such as characterized the recession of the ice border in the Wisconsin stage. Even along its 

 southern edge the knolls and ridges of the older drift can scarcely be said to form a moraine, for 

 they are loosely distributed and level surfaces predominate. Scattered over the older drifts 

 kames or sharp gravelly knolls rise either singly or in clusters to heights of 20 to 50 feet or 

 more above bordering nearly plane tracts ; many of them stand in low areas along the line of 

 preglacial valleys or on valley slopes, and in such situations some of them reach heights of over 

 100 feet. 



As already indicated, a few ridges of drift several miles in length have been developed. 

 One such ridge, in Morgan County, along Indian Creek southeast of Martinsville, is scarcely 

 one-half mile wide and is 50 to 100 feet or more in height. Another, within the limits of the 

 later or Wisconsin drift, in southwestern Shelby County, is known as Mount Auburn Eidge, 

 the village of Mount Auburn being on its crest; it is about 9 miles in length, 2 miles in width, 

 and 75 to 150 feet in height, with an irregular surface on which knolls rise abruptly 50 to 75 feet. 

 The mantle of later or Wisconsin drift is remarkably thin, the thickest deposit noted being 

 only 15 feet in depth. A third conspicuous ridge is Chestnut Ridge in Jackson County, first 

 described by Cox 2 and also discussed at some length by the present writer in Monograph XLI ; 

 its length is about 8 miles, its width but little more than one-half mde, its height 50 to 170 feet, 

 and its surface somewhat hummocky and irregular. Wells on the ridge show part of it to 

 carry a coating of till 50 feet or more in depth, but the greater part seems to be gravel and 

 sand. 



1 Tyrrell, J. B., Hudson Bay exploring expedition, 1912: Twenty-second Ann. Kept. Ontario Bur. Mines, pt. 1, 1913. 



2 Sixth Ann. Rept. Geol. Survey Indiana, 1S74, pp. 42, 56-57. 



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