June 13, 1902.] 



SCIENCE. 



953 



peneplain with a very strong element of 

 doubt. Mr. J. S. Diller saw the summit level 

 of the peaks from the top of Mt. Courtney, 

 altitude about 8,800 feet, and he felt very 

 strongly inclined to recognize the supposed 

 eroded base level. As for myself, T have never 

 before ventured to recognize a dissected pene- 

 plain on such slender evidence, but I think 

 that in time it will come to be an established 

 fact, although at present I shall refer to it 

 ■with a question mark. 



In the early stages of this investigation I 

 entertained the idea that the dissected pene- 

 plain ( ?) of the Sierra Costa summits was of 

 Cretaceous age, a portion of the same base 

 leveled land surface on the borders of which 

 after submergence the Horsetown and Chico 

 sediments were deposited, but reflection has 

 shown this to be improbable. The peneplain 

 ( ?) has suffered little deformation over an 

 area fifty miles long and twenty miles wide. 

 It is not likely that such an extensive tract 

 would remain intact while orographic disturb- 

 ances of the greatest magnitude were occur- 

 ring in its neighborhood. The inference is 

 that it has been developed at a later date if it 

 is really a feature of Klamath physiography, 

 and must be credited to the early Tertiary 

 times. 



That such a peneplain was developed out- 

 side of the Sierra Costa area subsequent to the 

 first post-Chico disturbance, over at least that 

 portion of the Klamath region which had been 

 covered by the Horsetown sediments, is evi- 

 denced by the behavior of the drainage system 

 of that region. The northward drainage of 

 the district between the Bully Choop range 

 and the Trinity Eiver was apparently inaugu- 

 rated by the post-Chico disturbance, but since 

 then there has been somewhat of a rearrange- 

 ment of the system. A trunk stream ought 

 to follow the line of basins marked by the four 

 Cretaceous remnants south of the Trinity 

 River, but, instead, all the main creeks cross 

 this line and traverse the structurally higher 

 ground on the north. Moreover, several of the 

 most prominent streams as the Hay Fork, Salt 

 Creek and the South Fork of Trinity River 

 cross the line along the structural ridges which 

 separate the basins, while one of the largest 



Cretaceous remnants constitutes the divide be- 

 tween two important creeks. Hay Fork and 

 Salt Creek. The Indian Creek Cretaceous 

 area is crossed by three parallel creeks, Indian, 

 Reading and Brown's, separated by low divides 

 where they are composed of the soft Cretaceous 

 strata, yet these creeks traverse a high broad 

 mica schist ridge in deep narrow gorges on 

 their way to Trinity River. The drainage 

 could not very well be more independent of 

 the structure either of the metamorphic rocks 

 or of the post-Chico deformation. It seems 

 that the surface of this region was planed 

 down and the streams then migrated and 

 adopted the shortest course to the great trunk 

 stream flowing west (or east) midway be- 

 tween the present Bully Choop range and the 

 Sierra Costa range. 



This rearrangement was not effected on the 

 late Neocene surface (correlated with the 

 Sierra Nevada peneplain), as the country of 

 that time at some distance away from the 

 main streams was too hilly. It seems rather 

 to have been the result of the disturbance of 

 an earlier peneplain — what more natural than 

 to correlate it with the supposed dissected 

 peneplain of the Sierra Costa summits ! 



In the extreme southwestern part of Oregon 

 and in the adjoining section of California, 

 Diller* has discriminated a dissected pene- 

 plain surface which truncates the tilted 

 Miocene strata and hence is of late Tertiary 

 age. It is best developed on the rocks of the 

 Coast Range region, but also penetrates the 

 Klamath region. Standing on one of the 

 higher summits of the Sierra Costa range, as 

 Mt. Thompson, altitude 9,345 feet, or Mt. 

 Courtney, altitude about 8,800 feet, this pene- 

 plain is well displayed. It is marked by a 

 general evenness of the surface of the moun- 

 tain ridges which in the far distance merge 

 into an apparent plain. It is as well preserved 

 as -one of the dissected peneplains of the East- 

 ern States. The whole country to the west- 

 ward of our position seems to have a general 

 and even slope toward the west-southwest. 

 There are a few monadnocks in sight, notably 

 Preston Peak near the Oregon line. 



* Coos Bay Folio of the Geologic Atlas of the 

 United States. 



