290 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
waters are visible for many miles up and down the fiord. Streams 
of considerable size sometimes plunge down from the rolling uplands 
in whose edge they seem to have just begun to cut a cleft. Ab¬ 
normal discordance of trunk and branch stream is, therefore, a 
strongly marked characteristic of the Norwegian drainage. The 
necessity for appealing to strong glacial erosion in explanation of 
this prevailing discordance, may be set forth as follows. 
Measure of Glacial Erosion in Norwegian Fiords. — The deep 
valleys of Norway, partly occupied by sea water, are incised 
beneath an uneven highland which bears so many hills and moun¬ 
tains that it makes little approach to a peneplain, yet which here 
and there shows so many broadly opened uplands between the hills 
and mountains that it may be taken to represent the well-advanced 
work of a former cycle of denudation when the region stood much 
lower than it stands now. As a whole, a mature or late mature 
stage seems to have been reached before a movement of uplift 
introduced the present cycle. Let us now make two suppositions 
regarding the work of normal river erosion in the preglacial part of 
the present cycle, in order to determine, if possible, how much addi¬ 
tional erosion must be attributed to ice in the production of existing 
forms. 
First, let it be supposed that the revived main rivers had incised 
their valleys to the depth of the present fiords in preglacial time, 
and that the discordance of main and side valleys now visible is the 
appropriate result of the youth of the present cycle. If we recall 
only the steepness of the fiord walls, this supposition might be justi¬ 
fied, and thus the amount of glacial erosion needed to develop exist¬ 
ing forms would be small. But it must not be forgotten that the 
fiords, although often steep-walled, are always broad, much broader 
than a young preglacial valley could have been at that stage of early 
youth when its side streams had not cut down to its own depth. 
Hence glacial erosion must, under this supposition, be appealed to for 
the widening of preglacial canyons, steep-walled and narrow, into the 
existing fiord troughs, steep-walled and broad. At the middle of the 
fiord troughs, the lateral erosion thus demanded would often measure 
thousands of feet, and that in the most massive and resistant crystal¬ 
line rocks. 
A second supposition leads to no greater economy of glacial 
action. Let it be supposed that the revived streams of preglacial 
time had reached maturity before the advent of the glacial period. 
In that case, the side streams must have entered the main streams 
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