1 8 Journal of Travel and Natural History 



gress of this work of denudation that the present contour of the 

 country is mainly to be traced. The process of excavation must 

 doubtless have been often and materially modified by underground 

 movements, the land sometimes rising or sinking and altering the 

 flow of water, one portion being removed under the protection of the 

 sea, and another part projected to be attacked by the waves and 

 weather. Moreover, earthquakes must have opened fissures, and 

 these may sometimes have altered the form of valleys, or deter- 

 mined the course of new ones. And even when the levelling 

 action of the waves and currents of the sea had smoothed off the 

 asperities due to such fractures of the solid crust, there may still 

 have been left inequahty of surface sufficient to guide the flow of 

 water and the progress of atmospheric waste along the line of the 

 fracture underneath. We may readily grant all this, yet, after all, 

 the influence of such underground movements, as it seems to me, 

 sinks out of sight when we come face to face with the great facts of 

 denudation. We are shut up to the conclusion first propounded by 

 the immortal Hutton : '' the mountains have been formed by the 

 hoUoAving out of the valleys, and the valleys have been hollowed 

 out by the attrition of hard materials coming from the mountains." 

 I have merely alluded to the forces of denudation. It would 

 be beyond the scope of the present brief sketch to do more. 

 Rain, springs, streams, rivers, frost, ice, waves, marine currents — 

 these are the agents ceaselessly at work in altering the face of the 

 country, and it is by their agency at diff'erent times and in different 

 degrees that, as I believe, the existing outlines of the country have 

 been mainly produced. By the action of the sea, a part of the 

 earth's crust which is upraised into land, is planed down, as the 

 Highlands and southern uplands must have been. As the land 

 thus levelled rises above the reach of the waves, it comes within 

 the sphere of the atmospheric agencies of waste. Rain falls upon 

 it and flows off along the inequaUties of the sea-worn surface. In 

 thus moving seawards, the rivulets necessarily deepen their 

 channels, and when these are fixed they continue to be chiselled 

 out deeper and wider. The merest accidents, and the slightest 

 impediments, may deteniiine at first the direction of the water- 

 courses ; but once determined they remain. As the land by up- 

 heaval gains in elevation and extent, the channels of its rivers 

 lengthen. Rain, springs, frosts, aid the action of the streams to 

 enlarge the hollows, and thus the runnels widen out by degrees 

 into valleys. By and bye, perhaps, sheets of snow and ice, such as 



