DAVIS: RIVER TERRACES IN NEW ENGLAND. 325 
tions of terraces are detailed, because it is the theory with its deduced 
consequences and not the facts that are on trial. Furthermore, it is only 
after the presentation of the theory that the pertinent facts can be con- 
veniently selected from among many others and that their bearing can 
be clearly appreciated. True, the attempt might be made independent 
of any theory to observe all facts thoroughly and to record them minutely, 
in the hope of including every item that could be asked for in the test- 
ing of whatever theory should afterwards be invented ; but under this 
method of work, items of minor importance are confused with those of 
major importance, and their recital becomes so long that the beginning 
is forgotten before the end is reached. As a matter of fact, observational 
study of this kind is notoriously incomplete. Indeed, the terrace prob- 
lem, like many others, gives striking illustration of the difficulty if not 
the impossibility of really seeing all the essential facts when only the 
eyes of the observer are trusted; and it illustrates at the same time ~ 
the critical power that is given to observation when it is directed towards 
significant points, instead of being allowed to wander in the vain hope 
of finding all the facts before theorizing is begun. For example, if it is 
not already manifest from the deductions of the preceding paragraphs 
that the terrace spurs formed of grouped cusps and the outcropping 
ledges that are associated with them are of particular significance, no 
doubt will remain on this point when the observations detailed in the 
following paragraphs are reviewed; yet in all that has thus far been 
written on this subject in New England, no description of grouped cusps 
is to be found, and no recognition of the significance and the generality 
of the relation between ledges and cusps is recorded. It is as if it had 
been thought that all parts of a terrace are equally significant ; that 
when ledges appear at the terrace base they are of no particular impor- 
tance. Even the citations made above from the writings of Edward 
Hitchcock do not show that that careful observer thought the ledges he 
described were of any more than local importance ; and certainly no later 
observer has been led by Hitchcock’s essay to understand the control 
that ledges exercise in determining terrace pattern and terrace preserva- 
tion. Yet after apprehending this control and discovering the suggestive 
relation that must cbtain between ledges and cusps, the cbserver no 
longer strays over his field ; he directs his steps and secures in the least 
possible time the greatest possible results. 
Largely deductive as the preceding portion of this essay is in its 
present form, the reader should not suppose that it was prepared inde- 
pendent of observation. The actual progress through the problem has 
