BY E. C. ANDREWS. 827 



(iii.) Recessio7i of great ice-flood, and subsequent smaller-flood action. 



The ground-moraines of tlie great ice-flood are too massive to 

 be moved bodily by the shrunken glacier. The moraines are 

 overriden simply and not used as weapons of corrasion; channels 

 are excavated in these deposits; their surfaces are rounded and 

 aggradation of pronounced surface-irregularities is characteristic. 

 In this way the writer would account for man}^ drumlin-mass 

 surfaces. Doubtless the great drumlin-masses were due to the 

 action of a great ice-flood; their present appearance is due to the 

 mere rounding of same by smaller ice-flood visitation. Other 

 conditions remaining unaltered, one must remember that the 

 evidence of numerous small advances of an ice-sheet succeeding 

 to a much greater glacial visitation admits of read}^ perception, 

 whereas, on the flood hypothesis, the evidence of such weaker 

 ice-mass visitations would be practically destroyed by a later 

 severe glacial attack. Therefore, on the assumption of a period 

 of stable equilibrium for a certain land-mass, one would expect 

 only with great difficulty to trace the history of minor glaciation 

 preceding a great ice-flood. 



A knowledge of this simple fact may, again, explain many 

 previous glacial difficulties. 



B. Ordinary Streams. 



All other geographic conditions being equal, land-areas 

 dependent for their water-supply on terrific storms of infrequent 

 occurrence should be reduced to base-level more quickly than one 

 of much heavier precipitation, but not subject to violent storms* 



Firstly, since tlie vegetation begotten of frequent rainfalls is a 

 great check on corrasive activities. 



Secondly, because the marked absence of great storms or 

 " cloudbursts " in the moist region affords little opportunity for 

 greatl}^ increased work. 



In the arid region the association of unprotected talus and 

 " cloudbursts " is productive of marvellous corrasive results. 



Example . — The graded condition of Western New South 

 Wales streams as compared with the immaturity of streams in 



