OBJECT OF THE MEMOIR. 207 



This subsidence continued until the sea reached the western base of the 

 Sierra Nevada and all or nearly all that part of California north, north- 

 west and west of Lassen peak, and almost the whole of Oregon was 

 beneath its waters. 



Relation of the Chlco and Wallala Beds. — The Wallala group of Becker 

 and White, exposed at Wallala, Mendocino county, California, and Todos 

 Santos bay of Lower California, has furnished a fauna containing only 

 ten reported species. The characteristic fossil of this formation, Coral- 

 liocharna orcutti, has since been discovered at San Diego, California, and 

 has been studied in the field by Dr W. H. Dall, who informs me that in 

 the same conformable series of strata with the Wallala fauna he found 

 Chico fossils. There is such an intermingling of Wallala and Chico 

 forms that it is not practicable to separate the Wallala and Chico beds. 

 It is the opinion of Dr Dall, which I am permitted to announce, that 

 the Wallala formation may properly be regarded as a phase of the Chico. 



In a collection of fossils made in 1888 at Stinking canyon, seven miles 

 southeast of Stillwater post-office, Shasta county, California, there are 

 three fragments, which were then supposed by the writer to be coral. Mr 

 Stanton has examined these specimens and recognizes them as either 

 Rudistse or Chamidre. The structure is very well marked, but the frag- 

 ments are not large enough to give more than the structure. It is so 

 characteristic a feature of these families that there can be little doubt as 

 to its identity. Furthermore, as Coralllochama orcutti is the only species 

 yet found in the Cretaceous of the Pacific states that has the peculiar 

 cellular shell structure, it is probable that the fragments in question are 

 of that species. This view of the case is corroborated by the fact that 

 Axinea veatchil is one of the most common shells of the Chico beds of that 

 region, and Dr Dall reports the same species, as well as Baculltes chlco- 

 ensis, at San Diego. It is evident, therefore, that the Wallala beds are 

 part of the Chico and require no further special consideration. 



Relation of the Chlco and Horsetown Beds. — Both of the formations are 

 well exposed in Tehama and Shasta counties, California, along the west- 

 ern side of the Sacramento valley. In 1888 and 1889 nine sections were 

 examined and two measured by Mr J. Stanley-Brown and the writer* 

 across the Cretaceous belt between Paskenta and Redding. 



The general strike of all the Cretaceous rocks in this belt is approxi- 

 mately north and south, and their dip is to the eastward, away from the 

 older rocks of the Yallo Bally mountains of the Klamath group. Sev- 

 eral small faults and folds, beside numerous irregularities in the dip and 

 strike of the strata at other points, were observed, but the irregularities 

 Avere always slight and of limited extent, and occur irregularly distributed 



* Am. Jour. Sci., vol. xl.Dec, 1800, p. 470. 



