268 R. Chambers, Esq,, on Glacial Phenomena 



degree, or ia some parts even of a half or quarter that amount, 

 ■whilst in existing glaciers the slope is seldom or never under 

 3°. The declivity requisite to insure a given velocity, bears 

 a simple reference to the dimensions of a stream. A stream 

 of twice the length, breadth, and depth of another, will flow 

 on a declivity half as great, and one of ten times the dimen- 

 sion upon one-tenth of the slope.'' 



If this be the simple principle concerned where there is a 

 declivity, it is easy to see that a very small declination from 

 the north to the south of Scandinavia, or of Northern Ame- 

 rica, would suffice to allow of a movement for the supposed 

 general glaciers of those regions, seeing that there is toler- 

 ably clear evidence of these glaciers having been on a scale 

 of volume immensely exceeding the glaciers of the Alps. 

 Judging from the abrasions they have left on hills, and the 

 height to which their detritus extends, they must have been 

 several thousands of feet in depth. 



But it appears as if it were not necessary that there should 

 have been any sensible inclination of the general surface over 

 which these supposed glaciers extended, if it be true, on the 

 hydrostatical principle announced by Professor Forbes, that 

 they would move under the influence of sufficient accumula- 

 tions in any quarter, in the directions in which they found 

 least resistance. Supposing such accumulations on circum- 

 polar grounds, there would be a spreading movement to the 

 south, liable to be affected to some extent by accidental im- 

 pediments ; in short, very much such a movement as the 

 glacial phenomena of northern countries lead us to expect. 

 To such an extension of the operations we now see, it is only 

 further necessary that the meteorological conditions should 

 have been such as to maintain the plasticity of the material ; 

 and this is a point on which we have assuredly no data that 

 would at once and decisively negative the demands of the 

 present theory. 



The nearest approach that we arc acquainted with in na- 

 ture, to the case here supposed, appears to be that afforded 

 by the phenomena of the land discovered by Sir James Ross 

 in the 79th degree of south latitude. " The vessels were 

 here stopped by a barrier of ice from 100 to 180 feet in 



