8 INTRODUCTION. 



be said that all the post-glacial faults should be 

 apparent; this, however, need not be the case, as 

 the sea subsequently has, in many places, modified 

 the surface of the glacial drift. 



In the following pages we will attempt to demon- 

 strate that, in general, valleys are connected with 

 faults or breaks, and that a valley or hollow could 

 seldom have been carved out unless there were cracks, 

 minor joints, or other shrinkage fissures, in which one 

 or other of the different denudants could work. The 

 majority of our examples will be taken from facts 

 observed by ourselves, principally in Ireland, but we 

 will also refer to what other observers have noted in 

 various countries. 



