278 PROCEEDINGS: BOSTON SOCIETY NATURAL.HISTORY. 
of valleys by their rivers. Thirty years is a long enough time for 
one to learn something new even about valleys, and on my second 
visit it was fairly startling to find that the lateral valleys opened on 
the walls of the main valley of the Ticino five hundred feet or more 
above its floor, and that the side streams cascaded down the steep 
main-valley walls in which they have worn nothing more than nar¬ 
row clefts of small depth. This set me wondering, not only as to 
the meaning of so peculiar an arrangement of valleys and streams, 
but also as to the reason why so peculiar an arrangement should 
not have sooner attracted attention as an exceptional characteristic 
of Alpine topography. Playfair long ago, when describing the 
relation of side valleys to their trunk, showed clearly that they had 
“ such a nice adjustment 
of their declivities that 
none of them join the 
principal valley either on 
too high or too low a 
level: a circumstance 
which would be infinitely 
improbable if each of 
these vallies were not the 
work of the stream that 
flows in it” (’ 02 , 102); 
yet the whole course of 
the passing century has 
hardlv sufficed to make 
V 
full application of this 
law. So much latitude 
is usually allowed in the 
relation of branch and 
trunk valleys that hun¬ 
dreds of observers, many 
of whom must have been 
cognizant of Playfair’s 
law, have made no note 
of the extraordinary exceptions to it that prevail in the glaciated 
valleys of the Alps. Even the most pronounced advocates 
of glacial erosion, with a few exceptions to be noted below, 
have been silent regarding the remarkable failure of adjustment 
between the declivities of lateral and main glaciated valleys. 
Indeed, in reviewing the writings of those who have accepted a 
Fig. 3. Val d’Osogna, a hanging lateral valley 
of the Ticino. 
