CORRELATIVE MOVEMENTS. 463 



There are also Aucella-b earing beds in that region that have been 

 referred by Nikitin ^ and by Aguilera and Ordonez j to the Jurassic, 

 which is said by the. latter authors to underlie the Cretaceous conform- 

 ablv. The Aacella? mentioned by Nikitin (Aucella pallasi, var. plicata, 

 and another with the form of .4. 2">''/7/a-s/, but with radiating sculpture 

 stronger than that of .4. bronni) are evidently like those of the California 

 Mariposa beds. They came from San Luis Potosi. Aguilera and Or- 

 donez list six species and three varieties oi Aucella under the head of 

 Jurassic fossils, referring them all to Russian species, some of which 

 occur in the older Aucella beds of Russia, while others, according to 

 Lahusen, are confined to the Neocomian. 



CORRELA TI VE MO VEMENTS. 



From the general correlation of formations already made some move- 

 ments of the land may be correlated. 



During the lower Cretaceous the whole western half of the North 

 American continent was subsiding and the sea transgressing. In most 

 places this movement continued with or without interruptions during a 

 part of the Upper Cretaceous. 



The extensive conglomerate of the Sacramento valley which marks 

 the basal portion of the Chico l)eds ma}^ have resulted from topographic 

 changes connected with the intrusion of the peridotites whose alteration 

 gave rise to the serpentines of the Coast range. It is not, however, ce*"- 

 tainly known that the eruption of the peridotites occurred at that time. 



Between the Horsetown and Chico l)eds in California there is no un- 

 conformity corresponding to that reported by Hill between the Upper and 

 Ivower Cretaceous of Texas. It is evident, however, that at the time rep- 

 resented by that unconformity there were widespread topographic changes 

 which are recorded, as noted by Dr Dawson,^ in the extensive conglom- 

 erate of the Dakota group as well as in the Upper Cretaceous of Queen 

 Charlotte islands and in the Chico beds of Oregon and California. 



The great post-Laramie disturljance noted b}^ Emmons § in the Rocky 

 mountain region corresponds to that represented by the unconformity 

 between the Chico and Tejon of northern California and Oregon. 



Resume and Conclusions. 



The discovery of Corallluchama orcutti in the basal portion of the Chico 

 beds at a number of points in the Sacramento valley completes the 

 demonstration that the Wallala l)eds are only a phase of the Chico. 



* Neaes Jalirb. fur Mineral. Geol. uiid Palwont., Bd. 2, 1890, p. 27;i 

 t Datos para la Geologia de Mexico, 1893. 

 X Am. Jour, of Sei., vol. xxxviii, p. 12.5. 

 g Bull. Geol. Soe. Am., vol. i, pp. 245-286. 



