INTRODUCTION. 



PHYSICAL geologists are at variance as to the forces 

 which have formed the present features of the earth's 

 surface. It seems to have been formerly a very 

 general belief that the shapes of the ground are more 

 or less due to movements in the crust of the earth 

 which have opened cracks and fissures, elevating some 

 portions and depressing others, and that to these 

 movements, combined with marine denudation, the 

 features of the surface of the earth are due. Hutton 

 seems to have been the first to broach the theory 

 that the surface has been principally sculptured by 

 meteoric abrasion ; and now most of the working 

 geologists in Great Britain seem inclined to dis- 

 regard unduly every other kind of action. During 

 many years of geological research, we have noted 

 certain relations between the different kinds of 

 " shrinkage fissures," breaks, lake-basins, valleys, 

 and other features of the earth; and although formerly 

 we accepted in a great measure the theories of the 

 " subaerialists," we are now led to believe that the 

 different denudants must act in combination; each 

 separately being incapable of doing much work, 



