GENERAL REVIEW. 247 



as we now behold on the higher mountains of the globe, 

 and within the arctic and antarctic regions. 



"We have arranged the period into three stages the first, 

 when the pre-glacial land (somewhat higher than the exist- 

 ing continents) began to receive the ice-sheet ; the second, 

 during which the ice-bound land subsided to the extent of 

 1800 or 2000 feet; and the third, during which the land 

 was step by step re-elevated, and the ice gradually dis- 

 appeared.* Each of these three stages must have left its 

 own proper impress ; but the second has obliterated so 

 much of the first, and the third so much of both, to say 

 nothing of what has been subsequently effaced by frosts 

 and rains and rivers, that it is always extremely difficult, 

 and often impossible, to discriminate their results. Hence 

 the great difficulty of reading aright the phenomena of the 

 glacial epoch ; and hence the conflicting views entertained 

 by geologists respecting their origin and arrangement. This 

 much, however, is certain, that the pre-glacial or pliocene 

 land -surfaces, wherever they are found, contain fossils; 

 that the first stage of the ice-epoch is characterised by 

 boulders little removed from their parent rocks, by finely 

 glacialised rock-surfaces, and by the true boulder-clay or 

 " till " of Scottish geologists, and is always unfossiliferous ; 

 that the second stage is characterised by re-assorted clays, 

 by more rounded and widely-dispersed boulders, and is also 



* While, for the sake of distinctness, we thus divide the ice-epoch 

 into three great stages, it must be borne in mind that there may have 

 been minor and local osciDations of sea and land during each successive 

 stage. Since the close of the glacial period such oscillations have taken 

 place more than once in our own islands, as proved by the " submarine 

 forests " that occur at so many places along the existing coasts these 

 forests, now partially under the sea-level, having evidently grown at a 

 higher elevation, been submerged to receive the silts that now cover 

 them, and again upraised to their present levels. Such minor oscilla- 

 tions tend to complicate, but they do not obliterate, the broader pheno- 

 mena of a period. 



