. Elementary physical geography . Fig. showing the result of an elevation, whichcaused the inner canon of the Colorado to he cut be-tween the older walls of the outer and broader valley. RIVER VALLEYS. 277. Plate valleys drowned by submergence beneath the sea. 278 PHYSICAL GEOGRAPHY. numerous islands are formed where the hilltops rise abovethe sea (Figs. 193, 211 and Plate 24). This entrance of thesea produces a reverse effect from that of elevation; forthe lower parts of streams may be dissected, and parts of onesystem may enter the ocean through separate mouths. Thisis v
. Elementary physical geography . Fig. showing the result of an elevation, whichcaused the inner canon of the Colorado to he cut be-tween the older walls of the outer and broader valley. RIVER VALLEYS. 277. Plate valleys drowned by submergence beneath the sea. 278 PHYSICAL GEOGRAPHY. numerous islands are formed where the hilltops rise abovethe sea (Figs. 193, 211 and Plate 24). This entrance of thesea produces a reverse effect from that of elevation; forthe lower parts of streams may be dissected, and parts of onesystem may enter the ocean through separate mouths. Thisis very well illustrated in many cases on the coast of Maine,and particularly well in the Chesapeake (Plate 24), which,with its tributary streams, represents a part of a river systemdrowned by the sea. When the strata are folded in the form of mountains,stream erosion is interfered with and often entirely the mountains rise, a dam is built in the path of therivers ; and unless their rate of down-cutting is as rapid asthe rate of elevation, which in most cases would not be true,the streams will suffer interruptions. If they persist intheir course, and cut their channels as rapidly as the moun-tains rise,
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