PREFACE. 



THE object of this volume is the geological history of 

 the British Islands regarded from a geotectonic and 

 geographic point of view, that is to say, it does not deal 

 with the rock-groups of which our islands consist, so much 

 as with the physical conditions under which they were 

 formed, the rocks themselves being described only so far 

 as is necessary for ascertaining whence their component 

 materials were derived, in order to form some conception 

 of 'the relative position of land and water during each 

 of the successive periods of geological time. 



The attempt made in a former volume on Historical 

 Geology to give brief accounts of the physical and geo- 

 graphical changes which took place during each period, 

 showed me that the subject required much more time and 

 consideration than I was then able to bestow upon it. 

 The restoration of the geography of any past period is a 

 problem of great difficulty, and the more remote that 

 period is from the present the greater does this difficulty 

 become. Most of the restorations given in the work re- 

 ferred to were very incomplete, and in the present state of 

 our knowledge many must remain so, but it seemed 

 possible that a more detailed consideration of the geo- 

 logical data, and a fuller discussion of the inferences de- 

 ducible from them, might yield better results, and might 

 at any rate pave the way for attaining to more complete 



