Prof. J. D. Forbes's Sixteenth Letter on Glaciers. 167 



well as in the harder part of the rock, a large Helix, perhaps 

 H. Mattiaca, Steininger, and more plentifully a small Helix ; 

 also Clansilia bulimoides and Dreissenia Brardi. 



From what we have said of the characters and contents of 

 these fossils and of the conditions under which they exist, it 

 results that all idea of their inorganic concretionary origin 

 must fall to the ground. Concretionary bodies are formed 

 from within outwards, but here exactly the opposite has 

 taken place ; lime in solution has permeated the parchment- 

 like shell of the egg, and has been gradually deposited on 

 its inside, and thus preserved the form of the egg after the 

 organic substance itself had disappeared. 



I consider, therefore, these fossils to be the eggs of snakes, 

 perhaps of a coluber ; they are, however, somewhat too large 

 for eggs of the colubers or lizards now existing in the neigh- 

 bourhood. 



Lizards lay their eggs in warm sand, but many snakes lay 

 them in moist ground or mud, even under water. Such 

 animals could have lived here, on the banks of the Maine 

 and the Rhine, and have deposited their eggs in the calcare- 

 ous mud, where, perhaps, an increase of calcareous matter 

 not only prevented the hatching, but furthered the petrifac- 

 tion of the eggs. — Quarterly Journal of the Geological Society, 

 No. xxii. p. 42. 



Sixteenth Letter on Glaciers, — addressed to Professor Jameson, 

 (1.) Observations on the Movement of the Mer de Glace down 

 to 1850. (2.) Observations by Balmat, in continuation of 

 those detailed in the Fourteenth Letter. (3.) On the gradual 

 passage of Ice into the Fluid State. (4.) Notice of an 

 undescribed Pass of the Alps^ By Professor J. D. FORBES. 

 Communicated by the Author. 



My dear Sir, — Having had the good fortune once more 

 to spend a few (though very few) days amongst the glaciers 

 of Chamouni last summer, I avail myself of your kind per- 

 mission to carry forward the account of my observations, 

 which has now, for a period of eight years, been regularly 



