nndiro.-l V;7'_J [March 21, 
rivor sysloin as it lias been o-ivon us by I'rofcssov Davis and 
acoe[it('(l as a working- basis by many !»'oooTa))liei-s. 
Conclusion. 
As alhivial terraces occur in numbers only under peculiar and 
special conditions, it is very difficult to find exam])les of many of 
the terraces 1 have enumerated in my classification. The simplest 
normal terr.ice due to the old age of the stream would seem to 
be impossible or at any rate highly improbable. Consequently 
we are driven to tlie conchision that a river will not exhibit 
terraces unless varying conditions act in such a manner as to 
bring about first the deposition of waste and later its partial 
removal. We need not be surprised at not finding terraces more 
frequently outside of the glaciated districts, for in no other case 
do we find for the reasons described above such favorable condi- 
tions for the development of alluvial terraces. Tlie secotid best 
set of conditions seems to be found in the regions that undergo 
frequent changes of climate, alternating between increase and 
decrease of precipitation. Hence, we may say that river terraces 
are not normal but accidental developments of a river system. 
Tt only remains to say in conclusion that it is often easy to 
confuse alluvial river terraces with other terraces, especiallj^ 
estuarine and lake terraces. Estuarine terraces may frequently 
merge into river terraces as the estuary becomes constricted into 
a true river. Lake terraces are especially confusing as they are 
often formed in re-entrants of a lake basin in such a manner that 
at first sight the basin seems to be part of a river system. They 
are, however, usually more continuous than river terraces. They 
appear not only in the re-entrants as benches of waste, but also 
upon exposed headlands as benches cut in the harder rocks by 
the force of the lake waves. As a lake is gradually drained away 
it may form terraces at every temporary Avater level and hence 
the terrace benches may be very numerous at any one locality on 
the margin of the lake basin. Sea benches are not apt to be 
confused with any other form of bench, and hence need not be 
considered in this connection. 
Note. — The literature on river terraces and alluvial terraces is 
very extensive. In addition to the writings of Davis, Gilbert, 
