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 and traversed them, 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 de la 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 ‘ 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 Hildon 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 mdentations 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- 
