ECONOMIC IMPORTANCE OF THE SHASTA GROUP. 203 



phosed to pseudodiabases, pseudodiorites, glaucophane schists, phthanites 

 and serpentines, and in them occur most of the quicksilver deposits. The 

 Aucella beds of the Sierra Nevada of California are intersected by numerous 

 auriferous quartz veins. They were referred to the Jurassic by Meek at a 

 time when Aucella was supposed to be exclusively Jurassic, and upon this 

 determination Professor Whitney based his assignment of the age of a great 

 upheaval. I showed that this upheaval followed the deposition of the Au- 

 ce//a-bearing beds of the Coast ranges as well as those of the gold belt, and 

 called it the post-Neocomian upheaval. Any further change in the horizon 

 to which Aucella is assigned Avill evidently modify correspondingly the desig- 

 nation of this great disturbance. The question whether the non-conformity at 

 Horsetown represents this Cretaceous upheaval or an earlier one is also im- 

 portant. 



Exposures at Riddles. — During the past field season additional informa- 

 tion has been obtained with reference to the relations of the two series. The 

 supplementary facts are furnished chiefly by a locality at Riddles, Douglas 

 county, Oregon, detected by Mr. W. Q. Brown while superintendent of a 

 nickel mine in the neighborhood. He was kind enough to send me numer- 

 ous instructive specimens. In June I visited Riddles and, with Mr. Brown's 

 assistance, made examinations of the stratigraphy and additional collections. 



The fossiliferous rocks at Riddles bear a very strong resemblance to those 

 of the Kuoxville series in California. There is the same prevalence of sand- 

 stones with subordinate layers of shale and occasional conglomerates and 

 limestones. The sandstone in both regions is usually very dense, thin-bedded 

 and of a dull greenish color. The strata at Riddles stand at high angles ; 

 they show considerable faulting and some metamorphism. Stratification is 

 often almost completely obliterated, but there is evidence of at least one 

 sharp fold and reason to suspect several. A few miles further north, at 

 Roseburg, the strata in a corresponding position are not fossiliferous, but 

 they are entirely similar to the more metamorphic portions of the Knoxville 

 group. While the general aspect of the rocks at Riddles is such as forcibly 

 to remind one of the Knoxville series, there are also differences. Limestone 

 is more abundant at Riddles than in any part of the early Cretaceous areas 

 in California which I have studied, and the conglomerates are much more 

 extensively developed. These seem to form the upper layer of the fossilifer- 

 ous series in Oregon. They are very coarse, and at points in the neighbor- 

 hood the mass is hundreds of feet in thickness. This conglomerate is evi- 

 dently extensive. Mr. Brown informed me that he had traced it continuously 

 for over 20 miles. It is noteworthy that the pebbles of the conglomerate 

 are largely composed of highly metamorphic rock, indicating a period of 

 dynamo-chemical action prior to the uplift of the fossil-bearing strata. 



The stratigraphical as well as the lithological relations of the beds in 



