Geology . overed, and less commonly still (if ever)superglacial. 3. Submorainic (basal) deposits were made chiefly by extraglacialwaters in advance of the first ice which affected the region where theyoccur. They were subsequently overridden by the ice and buriedby its deposits. Submorainic deposits, however, may have arisen inother ways. Subglacial waters may have made deposits of stratified ^our. of Geol., Vol. IV, pp. 948-970. 378 GEOLOGY. drift on surfaces which had been covered by ice, hut not by till, andsuch deposits may have been subsequently buried. The retreat of anice-sheet may have
Geology . overed, and less commonly still (if ever)superglacial. 3. Submorainic (basal) deposits were made chiefly by extraglacialwaters in advance of the first ice which affected the region where theyoccur. They were subsequently overridden by the ice and buriedby its deposits. Submorainic deposits, however, may have arisen inother ways. Subglacial waters may have made deposits of stratified ^our. of Geol., Vol. IV, pp. 948-970. 378 GEOLOGY. drift on surfaces which had been covered by ice, hut not by till, andsuch deposits may have been subsequently buried. The retreat of anice-sheet may have left rock surfaces free from till, on which the marginalor extra-marginal waters of the retreating ice, or of the next advancingice. may have made deposits of stratified drift. These may have beensubsequently covered by till during a re-advance of the ice in the sameepoch, or in a succeeding one. Still again, till left hy one ice-sheetmay have heen completely worn away locally before the next ice advance,. Fig. 506.—Diagram showing the intimate association of stratified and unstratified drift. so that stratified deposits connected with a second or later advancemay have been made on a driftless surface, and subsequently buried. 4. Intermorainic stratified drift may have originated at the outsetin all the ways in which supermorainic drift may originate. It be-came intermorainic by being buried in some one of the various waysin which stratified drift may become submorainic. Topographic distribution of stratified drift. — Though stratifieddrift is most abundant in valleys and lowlands, it is not confined tothese positions. Karnes are measurably independent of valleys andlowlands, and though eskers often show a tendency to follow valleys, THE PLEISTOCENE OR GLACIAL PERIOD. 379 they often disregard topography to the extent of crossing ridges anduplands a few hundred feet in height (200 to 400 feet in Maine l).Kame-terraces and deltas, also, are often well above the bottoms ofthe
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