DAVIS: GLACIAL EROSION. 
311 
tance that they deserve as witnesses to strong glacial erosion. 
Russell, in his “Glaciers of North America” (1897), makes no 
mention of discordant lateral and main valleys when discussing 
glacial erosion. James Geikie, in his “Earth Sculpture” (1898), 
allows to discordance of glaciated valleys hardly more than a second¬ 
ary importance in abstracts and quotations from Wallace’s accounts 
of Alpine lakes and from Richter’s essay on Noiway (see below), 
while the glacial erosion of lake basins is much more fully treated. 
Yet of all the facts that point to strong glacial erosion, none seem 
to give testimony so unanswerable as do hanging valleys. The fol¬ 
lowing extracts will serve to illustrate the gradually increasing 
recognition of their importance. 
Forbes on the Waterfalls of Norway. — Thinking that some 
interesting early observations on the hanging valleys of Norway 
might be recorded in Forbes’ book of travels in that country, I 
looked up waterfalls in his index and there found a reference to the 
cause of their profusion, which w r as stated as follows. 
“ The source of this astonishing profusion of waters is to be 
found in the peculiar disposition of the surface of the country so 
often referred to. The mountains are wide and flat, the valleys are 
deep and far apart.As the valleys ramify little .... and are 
wholly disconnected from th q fields [uplands] by precipitous slopes, 
it follows that the single rivers which water those valleys .... are 
supplied principally by streamlets which, having run long courses 
over the fields , are at last precipitated into the ravines in the form 
of cascades” (’ 53 , 251). 
Forbes was an excellent observer, yet this quotation is about 
equivalent to saying that there are many waterfalls in Norway 
because there are steep slopes over which the streams of the uplands 
must descend. The quotation deserves a place here if for nothing 
more than to show the advance of a half century in regard to w T hat 
constitutes the cause of a geographical feature. 
McGee on ‘Glacial Canyons , 1883. — The earliest article that I 
have found touching on this subject is the brief abstract of a paper 
read by McGee before the American Association in 1883, entitled 
“ Glacial Canons.” Observations in the Sierra Nevada led this keen 
observer to state that “ the effect of the temporary occupancy of a 
typical water-cut canon by glacier ice wall be to (1) increase its 
width, (2) change the original Y to a IT cross profile, (3) cut off the 
terminal portions of tributary canons and thus relatively elevate 
their embouchures, (4) intensify certain irregularities of gradient in 
