Page:Popular Science Monthly Volume 70.djvu/110

From Wikisource
Jump to: navigation, search
This page has been proofread, but needs to be validated.
hyphenated word was joined on the previous page because of the intervening image.— Ineuw talk 05:18, 14 October 2013 (UTC) (Wikisource contributor note)

photographs. They are distinctly U-shaped with smooth and regular walls. In spite of their breadth, which is a normal characteristic of mature valleys, the enclosing walls, especially in the lower portions, are oftentimes exceedingly steep and even precipitous, a characteristic of young, not of mature, stream valleys. Thus the same valley has the characteristics of two stages of development, the breadth of maturity and the steep-sidedness of youth.

It is evident that such conditions as those which characterize so many of the valleys of the Inside Passage can not be due to normal conditions of stream valley development. The discrepancies and anomalies are altogether too numerous and striking for such an explanation.


PSM V70 D110 Rock lip of a hanging valley in nunatak fjord.jpg

Fig. 7. The Rock Lip of a Hanging Valley Just West of the Nunatak in Nunatak Fiord. There is a vertical difference of 700 feet between the camera site and the lip of the valley. Photographs 9 and 10 were taken from this lip. Photograph by O. von Engeln.

If this is true of the origin of the valley forms, it follows that the present outline of the intricate maze of channels on this coast cannot be explained as a result of the drowning of normal stream-made valleys, as has been so universally believed to be the case.

It is now quite generally admitted that some of the features which characterize the 'Reaches' of the Inside Passage do not admit of explanation as a result of normal stream work. The feature that has been most uniformly admitted, to be abnormal is that of discordance of tributary and main valleys. The explanation of this hanging valley condition as a result of glacial erosion, which this paper is supporting, is not, however, so uniformly accepted; the chief objection of those who have not yet accepted it being their belief that glaciers are incompetent to perform such great work as would be required if hanging valleys are