INTERPRETATION OF LAND FORMS 127 



prove gradual progressive stream work, was in advance 

 of his English contemporary. Judged by contributions 

 to the Journal, Ly ell'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 range at 

 those points where the strata have been least inclined 

 and the height consequently is less." Speaking of the 

 magnificent stream-cut canyons of the Blue Mountains 

 of New South Wales, gorges which lead to narrow exits 

 through monoclines, Darwin says : "To attribute these 

 hollows to alluvial action would be preposterous." 11 



The influence of structure in the formation of valleys 

 is emphasized by many contributors to the Journal. 

 Hildreth in 1836, in a valuable paper, 12 which is perhaps 

 the first detailed topographic description of drainage in 

 folded strata, expresses the opinion that the West Vir- 

 ginia ridges and valleys antedated the streams and that 

 water gaps though cut by rivers involve pre-existing 

 lakes. Geddes (1826) 13 denied that Niagara River cut its 

 channel and speaks of valleys which "were valleys e'er 

 moving spirit bade the waters flow." Conrad (1839) 14 

 discussed the structural control of the Mohawk, the 

 Ohio, and the Mississippi, and Lieutenant Warren 

 (1859) 15 concluded that the Niobrara must have orig- 

 inated in a fissure. According to Lesley (1862) 16 

 the course of the New River across the Great Val- 

 ley and into the Appalachians "striking the escarp- 

 ment in the face" is determined by the junction of 

 anticlinal structures on the north with faulted mono- 

 clines toward the south; a conclusion in harmony 



