190 H. L. FAIRCHILD POST-GLACIAL UPLIFT OF X. E. AMERICA 



ness of the method and the truth of the results is the fact that in many 

 cases predictions of the location of deltas and of the height of the summit 

 plane have been closely yeriiied. 



In his discriminating and admirable work on the surficial geology of 

 Maine, Mr. George H. Stone recognized the utility of deltas in determi- 

 nation of water planes (68). He writes, P^ge 483, as follows: 



". . . If we should find, a great change in the coarseness of the sediments 

 taking place within narrow vertical limits, proving considerable slowing of the 

 waters at that point, and especially if this were observed in several valleys at 

 the same relative position to the lines of highest elevation, as determined by 

 observation of the coast beaches, we should have probable proof that the 

 streams of the land poured into the sea at those points. Thus far I have not 

 been able to apply the method satisfactorily, in part owing to the rarity of 

 known elevations in these valleys. Where the streams were large compared 

 to the breadth of the valleys it is doubtful if this method can be applied with 

 certainty. The broader and shorter valleys off the lines of the glacial rivers 

 are the most promising cases for the application of the method." 



The discrimination and caution observed in the use of deltas for find- 

 ing water planes will be described in the next chapter. 



Criteria for Determixation of Water Levels 

 classification and discussion of the criteria 



A brief discussion of shore features and the character of the primitive 

 or summit marine plane and the criteria employed in their study will 

 clarify this subject. 



In the order of importance or usefulness the classes of features which 

 may be used for the location of static water levels are listed as follows : 



1. Stream deltas. 



2. Bars; wave-built embankments. 



3. Wave-erosion lines; cliff and terrace; boulder fields. 



4. Drift- denuded surfaces; bare-rock areas. 



5. Wave-smoothed stretches; leveled kames and sand-plains. 



6. Valley plains. 



7. Marine fossils. 



The second class — bars of cobble, gravel, or sand — is the least common 

 in occurrence, but is ranked high because of the unequivocal, positive 

 character and reliability for even the less experienced student. However, 

 by themselves bars are no conclusive proof of initial or summit level, 

 even if they lie against slopes which offer no evidence of higher stand of 

 waters. Such negative evidence is unreliable. It is a mistake to rely 



