1871.] BOI^NEY POEMATION OV " CIEQXTES." 317 



produced ; and we must remember that in the most conspicuous of 

 those described above, the most compact rock forms the lowest stage. 

 To this question of cliffs in the bed of a glacier I shall return again; 

 for the present we may venture to assert that it is mechanically im- 

 possible for a glacier to sink into its bed so as to excavate a cirque 

 on so gigantic a scale. (6) But may they have been produced at some 

 bend in the ice-stream like the concavities in a river's course ? The 

 Creux de Champs and Am Ende der Welt certainly cannot be thxis 

 explained, because they are at the head of deep well-marked lateral 

 glens about a mile and a half long. The two cirques near the 

 Blacken Alp are inexplicable on this theory ; for the spurs from the 

 Blackenstock and Eothschutz would effectually shelter them from the 

 action of any glacier descending from the Surenen Pass (7562 feet); 

 and indeed the general contour of the ground suggests that their re- 

 cesses would be among the feeders of its neve, the rise from the 

 Blacken Alp to the last ridge leading to the Pass being comparatively 

 gentle. The Per-a-Cheval would offer less resistance to this expla- 

 nation than any other cirque, as it is on the concave side of the elbow 

 of a vaUey ; but as existing glaciers do not appear to produce such 

 marked effects in turning corners in their present beds, we may 

 fairly require much corroborative evidence before venturing to apply 

 this explanation here. 



There remains then the wider question to consider, Are we jus- 

 tified in supposing glaciers to have been the principal agents in the 

 excavation of the Alpiae valleys ? To prevent mistakes, let me state 

 that I do not now purpose to deal with that particular case of this 

 theory which is advocated by several distinguished foreign geologists, 

 and with so much ability in this country by Professor Ramsay, viz. 

 the excavation of lake-basins by glaciers, but rather with that wider 

 view to which, among others. Professor TyndaU has more than once 

 given the support of his experience and talent, especially in a paper 

 published in the Philosophical Magazine*. 



If we assign to glaciers any large share in the excavation of val- 

 leys, we may fairly ask that the main contours should lend them- 

 selves readily to this explanation, just as those of a river- valley, 

 although somewhat modified by other meteoric action, suggest run- 

 ning water as the tool that has principally fashioned them. Now, 

 as a rule, in the upper parts of Alpine vaUeys, where the glacial 

 action may be supposed most recent, and therefore least affected by 

 other denuding agents, we are struck by the steepness of the last 

 few miles up to the watershed, as compared with the inclination of 

 the rest of the bed. I will only mention a few instances out of 

 many — for the fact must have struck aU travellers — and will select 

 the first from the Dauphine Alps, not only because it is a district 

 very familiar to myself, but also because the valley of the Yen eon 

 runs, for its whole extent, with one most unimportant exception, 

 through remarkably hard crystalline rocks. Measured on the map, 

 this vaUey is about twenty miles in length from the spot where 

 the river debouches into the small plain above the Romanche, near 



* Phil. Mag. Ser. 4. toI. xsiv. p. 169. 

 VOL. XXVII. PART I. Z 



