632 JOHN LYON RICH 



7. Erosion. — A recent slight increase in precipitation is indicated 

 by the renewed cutting by the streams and by encroachment of 

 vegetation on the sand dunes. 



Conclusion. — In conclusion it is suggested that future corre- 

 lations of the high-level conglomerates, as well as of the later 

 terraces in the stream-valleys, can be most satisfactorily made on a 

 genetic basis. It will, in most cases, be impossible to trace these 

 features from one drainage-system to another directly. The only 

 basis for comparison is that, in general, like conditions will produce 

 like results, and if the conditions affect large areas, as for instance 

 climatic changes or great periods of planation or mountain-building, 

 their results will be equally widespread. 



