January 30, 1903.] 



SCIENCE. 



195 



acceptance in recent years, since the una- 

 nimity of these many witnesses and the 

 cogency of these generalizations have been 

 recognized. 



GLACIERS AS CONSERVATIVE AGENTS. 



Lest the opinion in favor of strong glacial 

 erosion should go too far, it is well to give 

 special attention to such articles as explain 

 by other processes the particular relation of 

 over-deepened main valleys and hanging side 

 valleys, to which so much prominence has 

 recently been given in this connection. Bou- 

 ney, writing on 'Alpine Valleys in Eelation 

 to Glaciers' (Quart. Journ. Geol. Soc, 

 LVIII., 1902, 600-702), recognizes the preva- 

 lently discordant relation of trunk and branch 

 valley in certain parts of the Alps, but con- 

 cludes, on the basis of ' personal examination 

 of every part of the Alps, of the Pyrenees, 

 the Apennines, Scandinavia, Auvergne, and 

 many other hill and mountain regions,' that 

 cirques are mainly the work of water; and 

 that in a system of valleys, denudation would, 

 on the whole, be checked where glaciers oc- 

 cupied the higher tributaries, and intensified 

 by the action of torrents in the principal val- 

 leys. Garwood, discussing the ' Origin of 

 Some Hanging Valleys in the Alps and Him- 

 alayas ' (Ihid., 703-715), also concludes that 

 glaciers ijrotect their floors. He explains cer- 

 tain striking examples of discordance between 

 trunk and branch valleys in the Alps as the 

 result of the accelerated erosion of the trunk 

 valley on account of the steepening of its 

 stream by a tilting of the region, while the 

 side valleys, at right angles to the direction 

 of tilting are not cut down, because their 

 streams are not tilted. Kilian presents some 

 ' Notes pour servir a la geomorphologie des 

 Alpes dauphinoises ' (La Geogrdphie, VI., 

 1902, 17-26), and insists that the hanging 

 lateral valleys of that district have been pro- 

 tected by glaciers while the main valleys have 

 been deepened by normal stream work. Lu- 

 geon adduces the occurrence of rock sills 

 that rise across certain Alpine valley floors, 

 notably a sill known as the Kirchet in the 

 Aar valley above Meiringen, and a similar 

 sill in the Rhone valley below Martigny, to 



prove that the ancient glaciers were not de- 

 structive agents; had they been, these sills 

 ought to have been removed; their presence 

 is a ' peremptory argument against the deep- 

 ening of valleys by glaciers ' (' Sur la fre- 

 quence dans les Alpes de gorges epigenetiques 

 et sur I'existence de bai'res calcaires de quel- 

 ques vallees suisses,' Bull, lahor. de geol., 

 Univ. de Lausanne, No. 2, 1901, 34 pp., excel- 

 lent plates). This author takes no account 

 of the hanging lateral valleys which are so 

 abundantly associated with the main valleys 

 of the Aar and the Rhone, and therefore 

 naturally enough gives much importance to 

 the rock sills, which in the theory of strong 

 glacial erosion are explained as residual hard- 

 rock inequalities in a much-deepened valley 

 floor. 



The manifest difficulty in the way of ex- 

 plaining hanging lateral valleys by the con- 

 servative action of the glaciers that once oc- 

 cupied them is the necessity of assuming a 

 systematic and persistent termination of 

 many independent glaciers at the mouths of 

 lateral valleys, for a period long enough to 

 allow the main stream to deepen its valley 

 by hundreds and to widen it by thousands of 

 feet. The difficulty in the way of accounting 

 for over-deepened main valleys by tilting, as 

 suggested by Garwood, is that in the plentiful 

 examples of tilted and therefore dissected 

 districts in non-glaciated regions, the side 

 streams cut down the side valleys about as 

 fast as the main stream cuts down the main 

 valley, and by the time the main valley is 

 well opened the side valleys enter it at grade, 

 in most accordant fashion. W. M. Davis. 



TEE MrsSOURI BOTANICAL GARDEN. 

 Froji advance sheets of the administrative 

 report on the Missouri Botanical Garden, 

 presented at the recent annual meeting of the 

 Trustees, it appears that the gross reven\ie for 

 the year was $124,431.89 and the total ex- 

 penditure $119,893.84, of which $25,352.64 was 

 spent for the maintenance of the garden 

 proper and $8,186.46 for improvements and 

 extensions in this department; $3,015.81 for 

 the herbarium; $6,595.40 for the library; 

 $5,086.67 for administrative expenses at the 



