Surface geology and agricultural conditions of Michigan . entually it covered the whole areaof Lake Superior and some of the bordering country and becamemerged with Lake Algonquin of the Huron Basin, as is indicatedin more detail below. The kind of material in the moraines throws considerable lightupon Die direction of ice movement for the moraines vary in theirrock constituents to correspond with (he changes in the rock for-mations over which the ice passed. In tin district underlain bycrystalline rocks to the west of the meridian of Marquette, thereis a greal preponderance of crystalline mat
Surface geology and agricultural conditions of Michigan . entually it covered the whole areaof Lake Superior and some of the bordering country and becamemerged with Lake Algonquin of the Huron Basin, as is indicatedin more detail below. The kind of material in the moraines throws considerable lightupon Die direction of ice movement for the moraines vary in theirrock constituents to correspond with (he changes in the rock for-mations over which the ice passed. In tin district underlain bycrystalline rocks to the west of the meridian of Marquette, thereis a greal preponderance of crystalline material, (See PI. Ill B)while in districts underlain by sandstone and limestone to the eastof the meridian of Marquette those rocks are Hie mos1 plentiful constitnents of the drill. A very bowldery moraine north of Republicis shown in PL III B. The moraines vary greatly in their topographic expression sothat a general description which will adequately set forth their Michigan Geological andBiological Survey. Publication 25, Geological Series 21,Plate B BOl LDERS ON MORAINE NORTH i REPUBLIC, MICHIGAN THE NORTHERN PENINSULA. 57 features can scarcely be given. In some cases they are made upof rather steep sided gravelly knolls among which are basins andsmall lakes with very little inclosed level land. In other cases theyare broken up into small strips or clusters of sharp knolls whichare separated by level or even swampy tracts. In such cases itbecomes somewhat difficult to map the exact position of the iceborder during the development of the moraine because of so manygaps or parts only feebly developed. By reference to the generalmap one may see how fragmentary and disjointed are some of themorainic- belts. In general, however, the morainic tracts are char-acterized by more numerous and sharper knolls than are foundon the intervening districts. THE OUTWASH APRONS, OR GRAVELLY PLAINS. The outwash aprons as already indicated are plains of sand andgravel which were formed on the
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