PREFACE TO THE SECOND EDITION. x i 



the Alleghany River had not before been fully appreciated, 

 since they are nearly continuous on the two-hundred-foot 

 rock shelf, and are often as much as eighty feet thick. It 

 seems probable, therefore, that the Alleghany and upper 

 Ohio gorge was filled with glacial gravel to a de])th of 

 about two hundred and fifty or three hundred feet, as far 

 down at least as Wheeling, TV. Va. If this was the case, it 

 would obviate the necessity of bringing in the Cincinnati 

 ice-dam (as set forth in pages 212-216) to account direct- 

 ly for all the phenomena in that region, except as this ob- 

 struction at Cincinnati would greatly facilitate the silting 

 up of the gorge. The simple accumulation of glacial 

 gravel in the Alleghany gorge would of itself dam up the 

 Monongahela at Pittsburg, so as to produce the results 

 detailed by Professor White on page 215.* 



Of European authorities who have recently favoured the 

 theory of the continuity of the Quaternary Glacial period, 

 as maintained in the volume, it is enough to mention the 

 names of Prestwich,f Hughes, J Kendall,* Lamplugh, || 

 and Wallace, A of England; Falsan,Q of France; Hoist, J 

 of Sweden; CrednerJ and Diener, J of Germany; and 



* For a full discussion of these topics, see paper by Professor 

 B. C. Jillson, Transactions of the Academy of Science and Art of 

 Pittsburg, December 8, 1893; G. F. Wright, American Journal of 

 Science, vol. xlvii, pp. 161-187; especially pp. 177, 178; The Popu- 

 lar Science Monthly, vol. xlv, pp. 184-198. 



f Quarterly Journal of the Geological Society for August, 1887. 

 X American Geologist, vol. viii, p. 241. 



# Transactions of the Leeds Geological Association for February 

 10, 1893. 



|j Quarterly Journal of the Geological Society, August, 1891. 

 A Fortnightly Review, November, 1893, p. 633; reprinted in The 

 Popular Science Monthly, vol. xliv, p. 790. 



La Periode glaciaire (Felix Alcan. Paris, 1889). 

 X American Geologist, vol. viii, p. 242. 



i Ibid., p. 241. 



1 Ibid., p. 242. 



