. Elementary physical geography;. rmed by the grinding motion of rock fragments at thebed rock of river channels. WORK OF AVALANCHES AND GLACIERS 167 ,S5 At the southern limit of the glacial ice sheet near theAtlantic, the drift occasionally takes the • form of longridges of bowlders—perhaps many miles in extent, and onehundred feet or more in height. In nearly every instancethese heaps aremoraines. Apart of LongIsland is prob-ably a termi-nal moraine, asalso are severalof the ridgesthat cross NewJersey. Manyof the lowridges extend-ing into thevalleys of Colo-rado are mo-raines. The finer drif
. Elementary physical geography;. rmed by the grinding motion of rock fragments at thebed rock of river channels. WORK OF AVALANCHES AND GLACIERS 167 ,S5 At the southern limit of the glacial ice sheet near theAtlantic, the drift occasionally takes the • form of longridges of bowlders—perhaps many miles in extent, and onehundred feet or more in height. In nearly every instancethese heaps aremoraines. Apart of LongIsland is prob-ably a termi-nal moraine, asalso are severalof the ridgesthat cross NewJersey. Manyof the lowridges extend-ing into thevalleys of Colo-rado are mo-raines. The finer driftof glaciation hasbeen strewn overthe northern Mis-sissippi Valley,and now consti-tutes the surfaceof the prairieplains. There are several strata of this drift, and the material differsmuch in productivity. In the northern part of Illinois a creek marksthe edge where two areas of drift join. On one side of the stream theland is worth about one hundred dollars per acre; on the other side,it is worth less than one-half as SPLIT ROCK: AN ERRATIC BOWLDER The bulternid-iree, growing jrom the cleft, is jorty years old. A remarkable form of drift is found in the rounded 168 PHYSICAL GEOGRAPHY blocks of stone strewn over the surface of the New Englandand Middle Atlantic States. These are commonly known aserratic boivlders. In mineral character the bowlders are ofmany kinds; those of the northeastern United States aremainly of granite. The most interesting feature aboutthem is the fact that they are unlike the rock in the localitywhere they are found; in some instances they have beenbrought from a long distance. Some of them are of enor-mous size; one, Split Rock, near Mount Vernon, New York,weighs not far from five hundred tons. Many years ago this bowlder broke into two parts along a cleavageplane. A butternut-tree grew up in the cleft and in time its trunkhas wedged the two fragments apart in the form of a V-shaped the northern part of Westchester County a huge
Size: 1378px × 1814px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyorkcscribnerss
