^26 Professor Agassiz on the Glacial Theory, 



and in the vicinity of Florence Court in Ireland. I have al- 

 ready said that the mounds of blocks, and the polished rocks, 

 are every where found to be intimately connected together ; 

 but I do not mean to say that polished rocks are not met w^ith 

 ■where there are no mounds, and that mounds are not met 

 with where there are no polished rocks ; for it may happen 

 that the rocks on which the ancient glaciers moved were, in 

 certain localities, very little calculated to retain the polish, 

 and that they may have lost their original lustre, while the 

 moraines composed of rocks of the elevated portions of the 

 valleys still exist on their flanks. It is thus that we see very 

 beautiful examples of mounds and ancient moraines in denary, 

 above Inverary Castle, although there are no 'polished rocks 

 in the immediate vicinity ; and it is thus that the magnificent 

 moraines of Cuilcagh, near Florence Court, are not accom- 

 panied by polished rocks, in consequence of the facility with 

 which the solid rocks of that locality are decomposed. On 

 the other hand, we frequently see beautifully polished rocks 

 without moraines ; and this is especially the case with the 

 very abrupt walls of narrow valleys, where the blocks have 

 fallen down at the period of the retreat of the ice, and have 

 reached the bottom of the valleys without resting on their 

 flanks. In such instances, instead of presenting the form of 

 moraines, the blocks are scattered irregularly over the sur- 

 face. We have an example of this on the northern walls of 

 Loch Etive. 



Dr Buckland and Mr Lyell, receiving the interpretation 

 that I have given of the facts quoted above, have also ob- 

 served a multitude of localities which, joined to those that I 

 have myself visited, form a very extensive net-work of traces 

 of ancient glaciers, stretching over the largest portion of 

 Scotland, a large part of Ireland, and the whole north of 

 England. 



II. Dispersion of erratic llocks in plains. — The phenomenon 

 of erratic blocks and polished rocks is not limited to the 

 chief groups of mountains, but is seen extending over the 

 whole surface of the country where it presents itself; with 

 this difference, that in the lower regions it assumes peculiar 



