118 M. Jc Bt'uumont on the Glacier Theory. 



This tublc, if farllier extended, would express completely 

 the features of the erratic phenomenon, and would be of utility 

 in interpreting its real nature. \Ve might be guided in the 

 choice of hypotheses by the comparison of this table with other 

 tables expressing similar features in certain natural pheno- 

 mena. 



At the end of my Memoir on Etna,* I have given a table of 

 the slopes of some glaciers. It would be desirable that this 

 table should be extended, in order that we might see what is 

 the lower limit of the slopes on which glaciers are capable of 

 moving. At present I am not acquainted with any glacier in 

 the Alps which moves for a considerable extent (a league for 

 example) over a slope of distinctly less inclination than 3°. 



I have also presented to the Philomathic Society a table 

 expressing the features of currents of water, by giving the 

 slopes of the courses of a great number of rivers and torrente. 

 These slopes have, so to speak, neither an inferior limit nor a 

 superior limit, because there are many vertical cascades, and 

 we find the Seine and the Rhone in certain parts of their course 

 flowing over slopes of very slight inclination, of four and of 

 ei'dit seconds. The mobility of the molecules of water accounts 

 sufficiently for the variety presented by the slopes of courses 

 of water. We may remark, however, that the study of courses 

 of water leads us to consider slopes of much smaller inclina- 

 tion generally than those of glaciers : the Rhone, between 

 Lyons and Aries, flows on a mean slope of 0.000553, or of 

 1' 51" ; the Rhine, between Bale and Lauterbourg, flows on a 

 mean slope of 0.000647, or of 2' 13". Now, the Rhine and 

 the Rhone are two very rapid rivers, and the Doubs, which, in 

 the environs of Besangon, flows on a slope of 0.001000, or of 

 3' 26", reaches about the limit of the slopes of navigable rivers. 

 This slope, however, is only about a fiftieth or sixtieth of the 

 smallest slopes of glaciers over spaces of some extent. 



The slopes of the upper limit of the erratic zone are inter- 

 mediate between those of glaciers and those of the great navi- 



* Aiinaks dcs Mines, 3d Series, vol. x., p. 565 (1836), and Mcmoircs pour 

 servir d tine dcscrii>tiun Geologiquc dc la France, vol. iv., p. 215. 



