Mat 24, 1907] 



SCIENCE 



835 



the lip of many hanging valleys is so little 

 trenched is strongly suggestive of the relative 

 ineflSciency of sub-glacial torrents; for pre- 

 cisely in such positions of sharply increased 

 descent should the torrents have been most 

 effective. 



W. M. D. 



HANGING VALLEYS IN ENGLISH LAKELAND 



Among the recent essays which explain 

 hanging lateral valleys otherwise than by 

 glacial overdeepening of the main valley ia 

 one by J. E. Marr, of Cambridge, England, on 

 ' The Influence of the Geological Structure of 

 English Lakeland upon its Present Features ' 

 (presidential address. Quart. Journ. Geol. 

 Soc.j London, LXII., 1906, Ixvi-cxxviii ; see 

 p. cvii-). The greater depth of the open 

 main valleys is here ascribed to normal ero- 

 sion on weak structural features called 

 ' shatter belts ' ; but under this explanation — 

 glacial erosion being disregarded — it is dif- 

 ficult to understand why the lateral streams, 

 which often mouth from 500 to 1,000 feet over 

 an open main valley floor, have accomplished 

 so little trenching of their hanging valleys 

 during the long period in which the main val- 

 leys were well widened by the slow processes 

 of general subaerial erosion. There are many 

 cases in non-glaciated districts where wide 

 longitudinal valleys on belts of weak rocks are 

 joined by narrow lateral valleys whose small 

 streams enter the main valley through belts 

 of hard rocks ; the Allegheny Mountains pre- 

 sent hundreds of examples of this kind: but 

 in practically all such cases, even when the 

 contrast in resistance of the hard and weak 

 rocks is strongly pronounced, the small lateral 

 stream has been able to cut its narrow notch 

 in the hard rocks down to accordant grade 

 with the main valley floor that has been opened 

 on the weaker rocks; for the widening of the 

 main valley by general subaerial erosion has 

 been a relatively long process even in its weak 

 rocks. The streams in the hanging valleys of 

 English Lakeland would then be exceptions to 

 this rule, if their hanging position is not to be 

 explained by the glacial overdeepening of the 

 main valleys. A number of cases of stream 

 capture and rearrangement are described by 



Marr in this connection; but as glacial ero- 

 sion is entirely omitted from the probletn, the 

 explanation by normal stream action alone 

 must remain in the same measure of doubt 

 as that which now obscures the explanation of 

 the rearrangement of various branches of the 

 Rhine in the neighborhood of Chur, Switzer- 

 land, by normal stream action, as stated a 

 score of years ago by Heim. W. M. D. 



HANGING VALLEYS IN GENERAL 



Since the convincing report on the glaciers 

 of Alaska by Gilbert (Harriman Alaska Ex- 

 pedition, nL, 1904), additional accounts of 

 main-valley troughs and hanging lateral val- 

 leys, regarded as the result of glacial erosion, 

 are given for the mountains of Alaska by E. 

 S. Tarr (' Glacial Erosion in Alaska,' Pop. 

 Scl Monthly, LXX., 1907, 99-119), and by R. 

 S. Tarr and L. Martin (' Glaciers and Glacia- 

 tion of Yakutat Bay, Alaska,' Bull. Amer. 

 Geogr. Soc, XXXVJII., 1906, 145-167; see 

 p. 159, figs. 17 and 18) ; for Norway by A. P. 

 Brigham (' The Fiords of Norway,' ihid., 

 XXXVni., 1906') ; for the Tian Shan moun- 

 tains by Eriederichsen (see these ' Notes,' 

 March 8, 1907); for the New Zealand Alps 

 by E. O. Andrews (' Some interesting facts 

 concerning the glaciation of southwestern New 

 Zealand,' Trans. Austral. Assoc. Adv. Sci., 

 1905, 189-205; good plates); for the Sierra 

 Nevada by A. C. Lawson (' The Geomorpho- 

 geny of the Upper Kern Basin,' Bull. Dept. 

 Geol., Univ. Calif., III., 1904, 291-376; see 

 p. 329) ; and for the Sawatch range of the 

 Colorado Rocky Mountains by L. G. Westgate 

 (' The Twin Lakes Glaciated Area,' Journ. 

 (Jeol, XIII., 1905, 285-312) and by the under- 

 signed (' Glaciation of the Sawatch Range, 

 Colorado,' Bull. Mus. Oomp. Zool., Harv. Coll., 

 XLIX., 1905, 1-11). 



' The pages of this article are not cited here, 

 because the reprint from which this reference is 

 made has been repaged, and consequently affords 

 no sufficient indication of its original place. If 

 editors of scientific periodicals still persist in the 

 troublesome habit of repaging reprints, it is to be 

 hoped that authors and reviewers will protest 

 against it. 



