formed by Ancient Glaciers* 



347 



recent visit from Prof. Agassiz afforded me an opportunity of 

 giving him the details of my own observations, and of hear- 

 ing from himself that the appearances I described have often 

 been seen by him on the sides of existing glaciers. I trust, 

 therefore, the subject may be thought of sufficient interest to 

 warrant a second communication. 



It would be difficult, as I know from experience, to make 

 intelligible to readers who have not visited Switzerland, the 

 real nature and appearance of a glacier. For years I had read 

 and thought much about them, and fancied I understood 

 them ; but, until I actually saw T and traversed them 5 I had no 

 correct idea of their real structure and appearance, and little 

 anticipated the powerful impression they are capable of 

 making upon the mind, when first examined under favour- 

 able circumstances. Saussure and other Alpine travellers have 

 given very lively descriptions of their wonderful appearance, 

 but the laws by which many of their phenomena are pro- 

 duced and regulated, were never satisfactorily understood 

 until Prof. Agassiz undertook their examination. The result 

 of five years* arduous and patient investigation by this illus- 

 trious savant will be found in papers read before the Geolo- 

 gical Society of France, and more at large in his £ Etudes sur 

 les Glaciers dela Suisse/ now just published. His discovery 

 also, since the meeting of the British Association at Glasgow, 

 of the traces of ancient glaciers in Scotland, Ireland, and the 

 North of England has been announced to the Geological So- 

 ciety of London, and is expected to appear in detail in the 

 forthcoming Number of the 6 Edinburgh New Philosophical 

 Journal/ It would, therefore, be extremely arrogant in me 

 to attempt to anticipate that communication ; but, as I have 

 already raised objections to the received theory from my ob- 

 servations on the Eildon Hills, it seems but fair, now that I 

 am enabled, from the familiar explanations of my distinguished 

 friend, to support as well as answer them by referring the 

 appearances to a more rational cause, that I should be allowed 

 to do so. 



As Prof. Agassiz entertains no doubt, from a perusal of the 

 article in Chambers's Edinb. Journal, and of my paper, that 

 most of the terraces on the hills in the neighbourhood of the 

 Tweed, are the morains of ancient glaciers, I shall confine 

 myself to a few particulars connected with their origin and 

 mode of formation. 



Glaciers occupy the gullies and lateral indentations of high 

 mountain chains ; and consist of immense accumulations of 

 spongy porous ice, or half-melted snow again solidified by 

 frost. Their texture near the apex or upper extremity, ap- 



