56 H. L. FAIRCHILD — ICE EROSION THEORY A FALLACY 



and Canandaigua. These great transverse valleys have their bottoms 

 obscured by drift, but the writer thinks that their rock bottoms are 

 higher than those of the north-south valleys, and that they represent the 

 work of an earlier drainage. 



The erosional history of the region from the time it was lifted out of 

 the Devonian or Subcarboniferous sea, down to the time of the Pleisto- 

 cene ice invasion, must have been eventful as well as long, and have in- 

 volved great changes in attitude. We may believe that the primitive, 

 consequent drainage from the Adirondack-Laurentian oldland was south 

 and southwest across the new coastal plain to the Mississippian sea. The 

 broad and high transverse valleys mentioned above may possibly be an 

 inheritance from that earliest drainage. Eventually the broad Ontarian 

 depression was produced as a subsequent valley along the outcrop and 

 strike of the very thick and non-resistant strata of the Lower and Upper 

 Silurian, and along with the production of this great east and west trunk 

 valley came the development of the (obsequent) drainage down the in- 

 face or north slope of the plateau (the Allegany cuesta) which has left, 

 as the finality of all the erosion, the north and south valleys that hold 

 the Finger lakes. 



The above is merely a suggestion of the events in the long and obscure 

 history ; but it seems probable that during the long exposure of the 

 region to erosive agencies, during the later Paleozoic, Mesozoic, and Ceno- 

 zoic eras, many changes must have occurred and the normal development 

 of the drainage have been modified by up and down land movements, 

 with more or less tilting of the area* 



The topographic forms and the valley relations have made this region 

 an enigma to the physiographers. If all the rock topography as left by 

 preglacial drainage were exposed to view the expert translators of physio- 

 graphic records might tell us most of the old history ; but, unfortu- 

 nately (or fortunately), the ice-sheet transgressed the entire region and 

 rubbed its load of drift into the valleys in very irregular manner, and 

 has badly obscured the preglacial topography. The precise relationship 

 of the valleys can not be known until borings determine the rock floors. 



The topography is anomalous, puzzling, and fascinating, and as it can 

 not be immediately explained by supposed laws of stream work some 

 students invoke the aid of ice and assume that glacial erosion is respon- 

 sible for the unusual features. 



*Some suggestions of the history may be found in the following writings : 

 A. W. Grabau : In New York State Museum Bull. No. 45, 1891. 

 R. S. Tarr : " The physical geography of New York state." 1902. 



M. R. Campbell : Geographic development of northern Pennsylvania and southern New York." 

 Bull. Geol. Soc. Am., vol. 14, 1903, pp. 277-296. 



