in Scotland and Parts of England. 279 



worn northern erratics, generally occupying a superficial po- 

 sition. Thus the sequence of events seems the same over 

 the island, though all are not everywhere expressed, — a re- 

 sult which no geologist will have any difficulty in accounting 

 for. 



It must be evident, when the whole subject of the superficial 

 deposits is thus analysed, that the vague general view which 

 is often taken of it by geologists, is one which can only be 

 entertained in defiance of facts. It is placed beyond all ques- 

 tion, that these deposits form the record, not of one epoch, 

 when our land was under a glacial sea charged with icebergs, 

 but of a succession of conditions in which the land sunk and 

 rose, and sunk and rose again, and during which phenomena 

 of very various character took place. It is not possible, in 

 the present state of the investigation, to speak with precision 

 of this succession of conditions and phenomena ; but 1 may 

 venture to point out what the facts suggest in the case, so 

 far as we are yet acquainted with them, leaving to future in- 

 quirers to make such modifications of my provisional view of 

 the matter as may appear necessary. 



The more general glaciation which has here been described, 

 with its attendant memorial of a detritus of striated local 

 blocks and clay, points to a wide extension of the circum- 

 polar ice, and a southern movement of that envelope, in 

 the course of which the surface was abraded and the detritus 

 produced. This icy sheet is shewn, however, not to have been 

 everywhere in precisely the same condition as a glacier of the 

 Alps, for there is a difference in the character of its detri- 

 tus. The boulder clay indicates a comparatively fluid state 

 of the ice, whether from passing across shallow seas, as it- 

 may have often done, or simply because the water which it- 

 self produced rested amongst its particles, instead of being 

 drained away, as it always is, in a valley glacier. There being 

 in the detritus of this glaciation no far transported blocks, 

 I attribute to the severity of the attrition to which they were 

 subjected. With this glaciation, moreover, is connected much 

 of that denudation which has hitherto been attributed exclu- 

 sively to floods. 



After this glacial period, the land had been partly sub- 



