882 Correspondence— W. B. Wright. 



present depth [and width] by pre-Glacial streams." Nothing is 

 easier than to draw such a diagram ; the difficulty comes in proving 

 that the Preglacial valley truly had the width and depth there 

 assigned to it. If it had any such width, its branch valley must have 

 had an accordant junction with it, but as a matter of fact the branch 

 hangs over the main valley. An additional difficulty would be found 

 in justifying the assumption that the profile given for the Snowdon 

 crest and for a cwm beneath it correctly represents the result of 

 normal erosion in Preglacial time ; yet such an assumption is made, 

 for no " solid black " is added to indicate that the mountain profile 

 has been perceptibly modified by glacial erosion. 



It is then concluded that " according to this interpretation the 

 topography of Snowdon at the beginning of the glaciation was 

 essentially the same as it is now ", and therefore that glacial erosion 

 has been of small measiire. Like the reticular system of fracture 

 valleys this conclusion can have little value until a never-glaciated 

 mountain district of altitude similar to that of North Wales is found, 

 in which the effect of a sub-recent uplift in reviving normal erosion 

 has been to produce huge cwms under sharp-edged mountain crests, 

 and half-mile-wide side valleys hanging over still wider main valleys, 

 with vigorous streams plunging down narrow clefts between the 

 two. Mountains and valleys of such forms do not exist outside of 

 deglaciated regions, and a great body of excellent evidence indicates 

 that their peculiar forms are the product of glacial erosion. 



W. M. Davis. 

 Harvard University, 

 Cambridge, Mass. 



Recent Sinking of Ocean Level. 



Sir, — Professor Daly's speculation in the June number of this 

 Magazine regarding the possibility of a recent worldwide sinking 

 of sea-level calls for exposition of the facts as regards the British 

 Isles. The writer feels somewhat at fault in the matter as he has 

 made a statement of results without evidence and expected it to be 

 accepted. Under the circumstances Profe^or Daly can hardly be 

 blamed for setting one statement against another, and considering 

 that perhaps the facts^may be as required by his theory. It should 

 be pointed out, however, that there is not really, as Professor Daly 

 has implied, any conflict between the writer's account of the so-called 

 25 ft. beach and those of Sir A. Geikie ^ and Hull. As regards 

 Kinahan's discussion of the raised beaches of Ireland, it can 

 confidently be said that what is not absolute error in it is so indefinite 

 as to have little meaning. To him anything served as evidence of 

 a shoreline, from a glacial corrie or a drift-bank to a limestone 

 escarpment. The lowest of his horizontal shorelines is by his own 

 statement only 4 feet above mean tide level, so that it is not clear 



^ Anniversary Address to the Geological Society, 1904. 



