Ui 



Robert A. Kehle: 



Orsw/J 6yfV.S.£. 



Fig. 6. 



A stage in the development of the intermediate cycle some time after the cessation of volcanic 

 activity. Note that the pre basalt streams are on the watersheds (infilled valleys)> 

 between the streams of the intermediate cycle. 



The rate of cutting back of the lateral streams was regulated, 

 in the first place, by the extensive lava field to the south, over 

 which all streams had to pass, and, in the second case, by infilled 

 tributaries which formed smaller confined lava fields at an angle 

 to the main field, at irregular intervals throughout its length. A 

 stream cutting back and encountering an infilled tributary worked 

 along the tributary lava field until by vertical erosion and sapping^ 

 the tributary lava field was breached; this usually occurred at or 

 near the main confined lava field. 



It is not to be assumed that lateral streams did not immediately 

 form along the whole length of the main infilled valley. They 

 existed from the first as streams of steep and variable gradients. 



