136 JOURNAL AND PROCEEDINGS 



that the escarpment face is not an artificially-made, uniform wall, 

 but a natural slope of more or less strength, thickness, hardness, 

 etc., and therefore more susceptible to weathering in some parts 

 than in others. It will be found, on examination, that the streams 

 have invariably broken through weaker parts of their boundary, 

 especially where they are traversed by faults, joints, etc. The 

 second is the date, geologically speaking, at which this inland fresh 

 water sea existed, from which the present system was evolved- 

 With the small amount of information that we at present have, and 

 in the present imperfect state of our knowledge of recent formations, 

 we can only state definitely the later Post-Pliocene as the period 

 when, by the series of uplifts, this lake was formed, and by the help 

 of more of these, it was finally dismembered and drained. 



