212 J. S. DILLER — GEOLOGY OF CALIFORNIA AND OREGON. 



thickness of conformable shales and sandstones that the writer regarded 

 them as not only contemporaneous but intermingled and belonging to 

 the same fauna. On Elder creek, therefore, the evidence clearly indi- 

 cates that the Horsetown beds are younger than the Knoxville, and 

 that between them there is a stratigraphic and fauna] continuity. 



Mr Becker and the writer* claimed that at Riddles, Oregon, AueeUa is 

 associated with ammonites and other forms of Horsetown age. The 

 writer visited Riddles four times, and, in company with Mr Will Q. 

 Brown, examined nearly all of the fossiliferous rocks of that region, but 

 has never been able to obtain AueeUa and Horsetown fossils from exactly 

 the same exposure. The rocks containing these fossils, however, are so 

 intermingled and related to each other structurally that there can be no 

 doubt that the fossils all belong to the same fauna. The valley of Cow 

 creek is eroded out of a more or less modified synclinal of Cretaceous 

 rocks. The older Aucella-henrmg strata are upon the sides. The strata 

 in which Horsetown forms are most abundant occur near the middle of 

 the valley, in the immediate vicinity of Riddles, where Aucella also 

 occurs. The whole set of strata appears to be conformable. 



The following forms have been identified by Messrs White and Stan- 

 ton in the collections made by Messrs Becker, Brown and the writer 

 near Riddles, Oregon : 



Aucella concentrica, Fisher. Pleuromya laevigata, Whiteaves. 



Amninriilrs tra*kii, Gabb. Pecten operculiformis, Gabb. 

 " batcsii, " " Californicus, " 



" brcweri, " Cardita translucidum, " 



Belemnites impressus, " Area breweriana, " 



In northern California the writer has found Ammonites traskii and A. 

 batcsii in the lower half of the Horsetown beds only, A. brcweri in the 

 upper half of the Horsetown beds, Pleuromya laevigata, Pecten operculi- 

 f or mis and Belemnites throughout the Horsetown beds, and the last two, 

 Cardita translucidum and Area breweriana, in both Shasta and Chico 

 beds.f 



* Bull. Geol. Soc. Am., vol. 2, pp. 201-207. 



fMr Will Q. Brown, who, under the writer's supervision, mapped a large part of the Cretai us 



rooks in Jackson and Douglas counties in Oregon, has recently made an important contribution 

 of new evidence. A collection which he generously made and transmitted at his own expense shows 

 Aucella and an Ammonitt in the same hand specimen, so there can be no doubt concerning their 

 association. Professor Hyatt has examined the specimen, and reports. December, 1892, that " the 

 Ammonites could by its external whorls be referred to either of the two groups Cosmoceras of the 

 upper Jura or Hoplitcs of the Cretaceous. By digging into the specimen enough of one of the 

 inner whorls was exposed to indicate that the A mmonites is one of the Cryptoa ras groups of HopliU s, 



and probably a true Cretacic species." Professor Hyatt adds that, as he has not yet l d able to 



find any species of this group with an aperture, his opinion stated above is only pnn isional, but the 

 evidence so far goes to show that one of the forms of Aucella occurs with a Cretaceous Ammonites. 

 The Ammonites, however, is very distinct from anything yet discovered in the Horsetow a beds else 

 where, it occurs in the basal portion of the beds which occupy Cow creek valley. 



