286 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The highest plain of a flight of terraces backs against the ascending 
slopes of the older valley side and accepts their outline as its border, as 
in Figure 6 ; while each lower terrace, as well as the existing flood plain 
— the “intervale” or “interval” of New Englanders — backs against 
the scarp of the next higher terrace ; thus the intermediate members of 
a flight of terrace steps possess similar but not necessarily parallel out- 
lines, front and back; the cusps between the curves all point towards 
the stream. The back border of a terrace is frequently followed by a 
marshy channel from which the terracing stream has been withdrawn 
by a short-cut or cut-off (as is more fully considered below) before the 
memes!) \ ae 
Fic. 6. 
channel was filled ; terrace plains thus characterized may slope gently 
away from the axis of the valley towards their back border, and if they 
are of moderate breadth the backward slope may be a relatively con- 
spicnous feature, as in the lower terrace in the middle of Figure 6. 
Terrace of this kind were called “glacis terraces” by Hitchcock (58).? 
They are of very common occurrence, and serve to show that the sudden 
withdrawal of the terracing stream from a roundabout channel to a more 
direct course has not been unusual. 
The scarp of a terrace connects the front border of the plain above 
with the back border of the plain below. Its sloping surface therefore 
1 Numbers in parentheses after an author’s name are page references to his 
writings, cited in the Bibliography. 
