CLASSIFICATION 77 



visional classification under four species, namely, stream-formed, ocean- 

 formed, diastrophic, and glacier-formed. 



STREAM-FORMED HANGING VALLEYS 



During the development of a river system a master stream may deepen 

 its valley more rapidly than certain of its tributaries are able to keep 

 pace, as has been explained by W. M. Davis and others, and the tribu- 

 tary valleys become discordant in gradient in reference to the main 

 valley with which they unite. The various ways in which such a result 

 is produced are well understood and need not be reviewed at this time. 



An example of a hanging valley due to stream erosion was recently 

 pointed out to me by M. S. W. Jefferson, near Ypsilanti, Michigan. In 

 this instance the Huron river, in deepening its channel, left a long narrow 

 point of land projecting from one side of its valley, and on the surface of 

 this cape-like projection and transverse to it is a segment of an old chan- 

 nel made by the Huron when flowing about 40 feet higher than now. 

 This fragment of an abandoned stream channel is now a hanging valley, 

 and at each of its ends there is a precipitous descent to the present flood- 

 plain of the stream that eroded it. 



On the border of the Huron valley, about 5 miles east of Ypsilanti, as 

 described by Isaiah Bowman,* there is a locality where the Huron river 

 in broadening its valley cuts into the upper portion of one of its own 

 tributaries. In this instance the portion of the tributary valley which 

 was " captured " and the neighboring portion of the abandoned segment 

 of the same valley respectively, were left " hanging " in reference to the 

 valley of the Huron, and illustrate a process by which a conspicuous 

 discrepancy between the bottom of a main valley and the bottom of a 

 tributary valley may be brought about. 



Each of the examples just cited may, as it seems, be logically classified 

 as varieties of hanging valleys due to stream erosion. 



OCEAN-FORMED HANGING VALLEYS 



When a valley, and particularly one with a steep gradient, is tributary 

 to the ocean, and a landward migration of the ocean shore occurs 

 through the action of waves and currents, the distal end of the valley 

 and its bordering uplands, may be removed, leaving its abbreviated up- 

 stream portion opening in the face of a sea cliff and its draining stream, 

 if one is present, discharging by means of a cataract into the sea. The 

 portion of a valley thus truncated would have the characteristic topo- 

 graphic features of a hanging valley, and might be of stream or glacial 



"A typical case of stream capture in Michigan." Jour. Geol., vol. xii, 1904, pp. 326-334. 



