108 Gregory — Progress in Interpretation of Land Forms. 



all their phenomena, and not a few geologists, especially those 

 of the Huttonian school, at whose head is Professor Playfair, 

 have till recently been of this opinion. . . . But it is now very 

 clear to almost every man, who impartially examines the facts 

 in regard to existing vallies, that the causes now in action, men- 

 tioned above, are altogether inadequate to their production; 

 nay, that such a supposition would involve a physical impossi- 

 bility. We do not believe that one-thousandth part of our 

 present vallies were excavated by the power of existing streams. 

 ... In very many cases of large rivers, it is found, that so far 

 from having formed their own beds, they are actually in a grad- 

 ual manner filling them up. 



Again ; how happens it that the source of a river is frequently 

 below the head of a valley, if the river excavated that valley? 



The most powerful argument, however, in our opinion, 

 against the supposition we are combating, is the phenomena of 

 transverse and longitudinal valleys ; both of which could not 

 possibly have been formed by existing streams." 



Phillips writes in 1829 : 7 "The excavation of valleys 

 can be ascribed to no other cause than a great flood of 

 water which overtopped the hills, whose summits those 

 vallies descend." 



Faith in Noah's flood as the dominant agent of erosion 

 rapidly lost ground through the teaching of Lyell after 

 1830, but the theory of systematic development of land- 

 scapes by rivers gained little. In fact, Scrope in 1830, s 

 in showing that the entrenched meanders of the Moselle 

 prove gradual progressive stream work was in advance 

 of his English contemporary. Judged by contributions 

 to the Journal, Lyell 's teaching served to standardize 

 American opinion of earth sculpture somewhat as fol- 

 lows : The ocean is the great valley maker, but rivers 

 also make them ; the position of valleys is determined by 

 original or renewed surface inequalities or by faulting; 

 exceptional occurrences — earthquakes, bursting of lakes, 

 upheavals and depressions — have played an important 

 part. Hayes (1839) 9 thought that the surface of New 

 York was essentially an upraised sea-bottom modified by 

 erosion of waves and ocean currents. Sedgwick (1838) 10 

 considered high-lying lake basins proof of valleys which 

 were shaped under the sea. Many of the valleys in the 

 Chilian Cordillera were thought by Darwin (1844) to 

 have been the work of waves and tides, and water gaps 

 are ascribed to currents "bursting through the ran^e at 

 those points where the strata have been least inclined 



