324 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



tematic attempt to discover the facts by which these deductions might 

 be con fin noil. 



In tbe case of a tilting, with fulcrum at the river mouth and at right 

 3 to the general river course, the maximum height of two-swing 

 terrace scarps would be found somewhere near the middle course of the 

 river; and the scarp height would thence decrease down-valley and up- 

 valley. It seems that, in such a terrace system as that of the Connecti- 

 cut, it may be possible to apply this test and thus gain from the 

 dimensions of the terraces a direct proof as to the kind of movement by 

 which the work of terracing was initiated, as well as a confirmation 

 of the evidence already in hand regarding the nature of postglacial 

 movement in the New England province. 



Relation of the Preceding Deductions to the Observations 

 described in the Following Sections. The facts presented in the 

 following sections are chiefly details of structure and form, directly 

 observable ; changes of form are occasionally noted, but these are of 

 relatively small measure. All these details are but the present members 

 of a long series of facts, every one of which might have been recorded, 

 had observers been living to witness them ; and then the origin of ter- 

 races would be fully understood. Bat the earlier members of the series 

 are hopelessly lost to observation from being prehistoric. In their 

 unavoidable absence, theory attempts to supply a series of conditions, 

 pictured by the reasonably guided imagination, which shall imitate the 

 series of past facts, and thus, as it were, call them to life, bring them 

 into the field of vision. The success of the theory is not to be measured 

 so much by the apparent reasonableness of its fundamental suppositions, 

 or by the definiteness with which various imaginary consequences may 

 be deduced from it, as by the accuracy with which the observable 

 members of the deduced consequences imitate the facts of actual occur- 

 rence. The greater the number of peculiar categories of observed facts, 

 the greater the probable correctness of a theory whose deduced conse- 

 quences can match all of them. Hence the importance of minute 

 observation and careful generalization on the one hand, and of accurate 

 and detailed deduction on the other. Hence also the importance of 

 carefully distinguishing these unlike processes in order that their results 

 may be systematically confronted in an unprejudiced comparison. The 

 elaboration of the deductions in the preceding sections therefore seems 

 to be as necessary a part of the study of terraces as is the accumulation 

 of observations for presentation in the following sections. 



The theory of terracing has here been presented before the observa- 



