Mr H. Goodsir on the Genus Cuma. 119 



gable rivers. They are of an inferior order to the slopes of 

 glaciers, whereas they are of the same order as those of the 

 most impetuous torrents. These slopes, without any excep- 

 tion, would be very considerable for rivers of a few yards in 

 depth, and they would be enormous for masses of water having 

 a section equal to those determined by the limits of the erratic 

 zone in the valleys of the Alps, sections having a depth of 

 from 800 to 1000 yards ! With such slopes and such sections, 

 the currents of water would \\^\c frightful rapidity ; currents of 

 mud, even the most viscid, forming nants sauvages on a gigan- 

 tic scale, would also acquire enormous rapidity, and be capable 

 of prodigious effects. 



The rapidity of a liquid augments with the slope of its sur- 

 face, and with the depth of its section ; of this the rapidity 

 acquired by all rivei's when flooded is a demonstrative proof. 

 On the contrary, it is doubtful if a very thick glacier expe- 

 riences less difficulty than a thinner one in its movement over 

 a gentle slope. This is an essential point to which attention 

 ought to be paid in the comparison of these two classes of 

 transporting agents. Acquired velocity has no share in the 

 movement of glaciers. 



Such a difference exists between the rCgime of ice in move- 

 ment and that of running water, that by preparing three com- 

 parative tables, one of the above-mentioned features of glaciers, 

 another of those of streams of water, and a third of those 

 of erratic phenomena, a powerful aid would be obtained in 

 determining the cause of the last. 



Description of the genus Cuma^ and of Two Nciv Genera nearly 

 allied to it. By Henry D. S. Goodsir, Esq. Communi- 

 cated by the Author.* (No V.) With Plates. 



During the summers of 1841 and 1842, I obtained a num- 

 ber of crustaceous animals, which I arranged promiscuously 

 under the genus Cuma of M. Edwards, it being my intention 



* Kcad before the Wcrncrian Natural History Society, Dec. 10, 1842. 



