Viii CONTENTS. 



Page 



V. FOURTH LETTER ON GLACIERS. Addressed to PROFESSOR 



JAMESON [1842] . -, .26 



Change of Level and General Appearance of the Glacier in the 

 month of September... Collapse of the Walls of the Cre- 

 vasses.... Moulins.... Veined Structure.... Direction of the 

 Crevasses... Both Veined Structure and Crevasses renewed 

 from time to tune... The Motion of a Glacier resembles that 

 of a Viscid FluidObjections to the Dilatation Theory... 

 What the Cold of Winter may be supposed to accomplish. 



VI. FIFTH LETTER ON GLACIERS. Addressed to the Bight 



Honourable EARL CATHCART [1844] . . . 35 



Motion of the Mer de Glace in the year 1842-3. . .Winter Move- 

 ment... The Veined Structure reproduced at the foot of an 

 Ice Cascade.., Cuts the Medial Moraines... Wrinkles in the 

 Ice of the Glacier du Geant and that of Grindelwald, 

 probably corresponding to the position of the Dirt-Bands... 

 An Ancient Moraine at Chamouni. 



VII. SIXTH LETTER ON GLACIERS. Addressed to the Bight 



Honourable EARL CATHCART [1844] ... 43 



Analogies of Glaciers to Lava Streams,,.. Observations on 

 Mount Vesuvius... Moraines of Lava Streams. - Some Objec- 

 tions to the Plastic or Viscous Theory of Glaciers considered 

 ,..Verticality of Crevasses accounted for. 



VIII. SEVENTH LETTER ON GLACIERS. ON THE VEINED STRUC- 



TURE OF THE ICE, Addressed to the Bev. Dr. WHEWELL, 

 Master of Trinity College, Cambridge [1844] . . 56 



Mechanical Considerations tending to explain the Forms of the 

 Veined Structure under different Conditions. 



IX. EIGHTH LETTER ON GLACIERS. Addressed to PROFESSOR 



JAMESON [1844] 61 



Observations on the Motion of the Glacier of Aletsch, . .Experi- 

 ments on the Plasticity of the Ice of the Mer de Glace, by 

 Observing the Distortion of a Limited Space of Ice devoid 

 of Crevasses... Movement of a Glacier of the Second Order 

 8000 feet above the Sea. 



