xii PREFACE. 



to elicit the truth where it has here been misrepre- 

 sented or overlooked. 



In many instances that have come under review in 

 the examination of these islands, it would have been 

 desirable to have referred to corresponding appear- 

 ances on the continent of Europe, or in other 

 analogous situations ; as such comparisons must have 

 materially increased the general interest of the facts 

 here described. But those countries are unknown 

 to me ; and in attempting to compare my own ob- 

 servations with those recorded by authors, I have been 

 unable to satisfy myself respecting their corre- 

 spondence ; partly from uncertainty as to the use 

 of terms, partly from a doubt whether, in many cases, 

 the observations in question were purely practical, 

 and, occasionally, from the broad and abstract mode 

 in which those statements are made, and the rapid 

 and general manner in which the examinations appear 

 to r have been conducted. 



With respect to the observations of British geolo- 

 gists, I have, for other reasons, rarely been able to 

 derive advantage from them. These have been prin- 

 cipally limited to the secondary country of England, 

 while the present relate chiefly to the primary 

 rocks. 



Further, as the light under which many of these 

 facts have appeared to myself, has sometimes differed 

 from that in which they have been viewed by others, 

 comparisons of such a nature would have inevitably 

 led to a species of controversial examination which it 

 seemed desirable to avoid, and which would have 

 prolonged the Work without much apparent utility. 

 Where it was impossible to avoid such remarks with- 



