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 obtain between ledges and cusps, the observer 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 



