On (he Movement of Glaciers. 175 



thought formerly to have covered, but are rarely seen to form the 

 dykes or moraines seen at the terminations of glaciers at present in 

 existence ; this fact apparently proving that they must have com- 

 menced their decay very shortly after their formation. 



The author stated several other arguments in favour of the truth 

 of the sliding theory ; from all which he inferred, that the move- 

 ment was not a continuous but an interrupted process ;— that when 

 the melting of the sides of the mass detached it from its attachment 

 to the sides of the valley, and it became undermined below, by the 

 melting of its base, the force of gravity, unresisted by friction, was 

 brought into play, and it made a sudden progressive movement 

 (which might be only an inch or several feet), when it remained at 

 rest, till the same causes produced a renewal of the same result. 

 He shewed, that though many parts of these icy masses were nearly 

 level, all the upper portions, and many of the lower, were lying over 

 such inclined planes, that gravity could exert its full power in their 

 propulsion ; and as the whole icy mass was tolerably solid and con- 

 tinuous, the greater movement of one portion was comnmnicated 

 more or less throughout its whole length, and tended to urge for- 

 wards and downwards those parts which had less tendency to move 

 onwards of themselves. 



The author also endeavoured to account for the advance of one 

 glacier, and the retirement of another alongside of it, by supposing 

 that it was caused by the snows being drifted away from the one 

 valley exposed to the blast, and from which the glacier, which was 

 retiring, descended, and being deposited in deep wreaths in the other, 

 which was probably more sheltered, and from which descended the 

 glacier, which was making destructive advances. The increased ac- 

 cumulation of snow, by furnishing a supply greater than the waste, 

 caused the one glacier to advance, whilst the other retired, in conse- 

 quence of the waste at its lower extremity exceeding the supplies 

 from above. 



2. On Plague, in relation to the question of its Nature, whe- 



ther or not a Contagious Disease. By John Davy, M.D , 

 F.R.S.S. L. & E. 



3. Analysis of Two New Minerals of the Zeolite Family 



