320 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
stretches, and frequently heading in a corrie whose floor may hold a 
small rock-basin tarn. In longitudinal profile, the floor of a valley 
often consists of two or three stretches of relatively gentle slopes, 
or sometimes of basin form and then holding lakes, separated by 
relatively sudden descents. Tributary valleys mouth at a consid¬ 
erably higher level than the floor of the main valley, (’ 99 , 196-199). 
Gilbert on Alaskan Valleys , 1899. — A valuable contribution to 
the origin of hanging valleys will be found in a report on the Harri- 
man Alaskan Expedition of 1899, to be published shortly. A gen¬ 
eral statement of results was made by Gilbert during the session of the 
Geological Society of America in Washington, December, 1899, when 
the importance of the hanging lateral valleys in the Alaskan fiords, 
and their bearing on the problem of glacial erosion, was clearly set 
forth. 
JBlanforcl on /Scotch Glens , 1900. — The only article that I have 
found on hanging valleys in Scotland is by Blanford, “ On a partic¬ 
ular form of surface, apparently the result of glacial erosion, seen on 
Loch Lochy and elsewhere.” The “ particular form ” here referred 
to is the smoothness of the sides of the Great Glen of Scotland, a 
feature that may be held analogous to the smooth rock walls of the 
Norwegian fiords, and to the spurless basal cliffs of the glaciated 
Alpine valleys. It is inferred that in preglacial time the streams of 
the lateral glens were separated by advancing spurs which buttressed 
the sides of the Great Glen. Now the spurs seem to have been 
truncated, producing the smooth and even sides of the glen, to 
which attention is especially directed. The lateral glens are described 
as at present opening a thousand feet above the floor of the Great 
Glen, whose smoothed sides are very little eroded by the descending 
tributary streams. The change from the inferred preglacial form is 
conservatively taken to indicate a glacial erosion of u at least 250 or 
300 feet of rock” ( 1900 , 198-204). 
Ilershey on Sierra Costa , California, 1900. An article by Her- 
shey, already referred to above, is the latest contribution to the sub¬ 
ject in hand. In following up a valley in the Sierra Costa in 
northwest California, it is at first V-shaped, with jagged ledges 
between sharp-cut ravines on the sides, and hardly wider at the 
bottom than the stream that drains it. On reaching the stretch 
once occupied by a local glacier, the valley becomes an open IT- 
shaped trough, with smooth slopes free from ravines and spurs. 
Above the limit of glacial smoothing, the mountain sides are still 
deeply scored with ravines and jagged with outcropping ledges. 
