CANYON AND DELTA OF THE COPPER RIVER, ALASKA 699 



Superior, partly removed by later glaciation from the northeast, confirming 

 Mr. Leverett's idea of a movement of ice southward from the Patrician region, 

 causing the Iowan till sheet. 



CANYON AND DELTA OF THE COPPER RIVER IN ALASKA 

 BY LAWRENCE MARTIN 



(Abstract) 



The canyon by which the Copper River crosses the Chugach Coast Range in 

 Alaska is over 100 miles long and 4,000 to 7,000 feet deep, the width varying 

 from 2% to 4 miles. The heights specified are attained within 1 to 3 miles of 

 the river. The Copper River Canyon is, therefore, deeper in places than the 

 Grand Canyon of the Colorado, with which it forms numerous contrasts be- 

 cause of profound glacial erosion. At its northern end is Wood Canyon, which 

 is apparently due to postglacial incision following glacial diversion of the 

 Copper River, rather than rejuvenation through warping, as postulated by 

 Spencer. The former Copper River Glacier widened and deepened this canyon 

 tremendously, as is shown by oversteepened valley walls, truncated spurs, and 

 hanging valleys. The grade of the river in the canyon is 3^ to 15 feet to the 

 mile. The canyon terminates in a flaring lower section interpreted as a former 

 fiord, now filled by the glacial sediments of the Copper River delta, whose 

 area exceeds 500 square miles. On this delta detailed measurements of width 

 and depth and of the rate of stream flow in the several distributaries furnish 

 important data on the carrying power of glacial streams. Comparative studies 

 in several years show the rates of deposition and of erosion. Borings by the 

 railway engineers show the nature of outwash material below the surface at 

 several positions and depths on the delta. Vegetation below present sealevel 

 in these borings proves recent sinking of the land. The existing glaciers of the 

 Copper River Canyon dominate the river in places, causing the deposition of 

 outwash gravels in one area of over 50 square miles above a glacier dam. The 

 distribution of present-day vegetation in the canyon suggests a. recent pre- 

 historic period of glacial expansion. 



SUBMARINE CHAMMCYPARIS BOG AT WOODS HOLE, MASSACHUSETTS, AND 

 ITS RELATION TO THE PROBLEM OF COASTAL SUBSIDENCE 



BY DOUGLAS W. JOHNSON 



(Abstract) 



At Quamquisset Harbor, near Woods Hole, the sea has cut into a chamrecy- 

 paris bog, the base of which is 13 feet below mean sealevel. This submarine 

 bog has been regarded by some as an especially good proof of recent coastal 

 subsidence, and therefore deserves special attention. According to Bartlett.i 

 the bog occupies a kettle hole, and represents successive layers of vegetation 

 continuously built up to the surface of a ground-water table which rose higher 

 and higher as the land subsided. This subsidence required something over 

 2,000 years, and is still in progress, the sea having recently cut into the bog 



1 Rhodora, vol. xi, p. 221 ; Science, vol. xxxiii, p. 29. 



