i;6 



University of California. 



[Vol. 2. 



featureless plain," and to the occurrence of deep soils and residual 

 gravels, there could be little chance of mistake in calling the surface 

 a peneplain. Adjustment of the stream courses might be found in 

 regions which had not reached the peneplain condition before eleva- 

 tion, but if found in conjunction with the other features just men- 

 tioned, it would form confirmatory evidence of the existence of a 

 peneplain. 



Thus, while, as has already been shown, most of the features of 

 so-called peneplains may be explained in other ways, the occurrence 

 of all of them together should be positive evidence of the existence 

 of a peneplain. A truncation of the summits, at a roughly uniform 

 altitude, with the occurrence of stream gravels here and there upon 

 the uplands, little below the general level, would form strong pre- 

 sumptive evidence of peneplanation.* Systematic and widespread 

 truncation of hilltops, in regions of disturbed rocks, where the 

 bedding is beveled across, can be explained only by actual planation 

 in some form, through either marine or subaerial erosion. 



As to buried peneplains, even greater caution is necessary in 

 pronouncing on the evidence, which in the nature of the case must 

 be very meager. Most of the cases described as buried peneplains 

 rest, in the opinion of the writer, on very doubtful evidence. It is 

 to be noted that the buried peneplains described are never dissected, 

 while those with which we are familiar on the surface are all dis- 

 sected to a greater or less degree. This is only natural, as it would 

 be almost impossible to determine a buried peneplain if it had suf- 

 fered much dissection before burial, while those which were sub- 

 merged without dissection might still yield definite evidence as to 

 their character. 



Further, the hypothesis of beveling is not intended to take the 

 place of any other causes which may result in an effect of plana- 

 tion — such as horizontality of bedding, extensive lava sheets or 



*It has been suggested to me by Professor Lawson that planation (see 

 Gilbert: Report on the Geology of the Henry Mts., p. 121) might take place 

 without an approach to ultimate base-level, by the meandering, at considerable 

 elevations, of streams in soft rocks, above a local base-level in very hard rocks. 

 The evidence just described might indicate such a condition of things, since in 

 itself it would be insufficient to determine whether or not there had been an 

 approach to ultimate base-level. 



