1916] 



Packard: Cretaceous of Santa Ana Mountains 



155 



therefore have had but little weight in determining the character 

 of the Chico faunas. Temperature would be a factor in so far as it 

 was associated with oceanic currents, the courses of which are deter- 

 mined largely by the distribution of land and water. 



There appears to be little evidence that salinity played an im- 

 portant role in determining the peculiar features of these two faunas, 

 for neither in the Santa Ana Mountain basin nor in that of the 

 Sacramento Valley do we find indications of brackish-water conditions, 

 except very locally during comparatively short periods of coal 

 formation. 



The direct and indirect effect of the type of the bottom is a 

 generally recognized factor influencing the life upon the floor of the 

 sea. A comparison of these basins of deposition reveals the fact that 

 the strata of the more southern one are more conglomeratic than are 

 those of the northern basin. The fauna as well as the lithology 

 indicates that the Cretaceous beds of the Santa Ana Mountains were 

 deposited largely within shallow waters. The species types from Chico 

 Creek and the considerable amounts of carbonaceous material also 

 argue for shallow-water conditions within the northern basin. It thus 

 appears that the fauna! differences can not definitely be attributed 

 to differences in the character of the bottom. However, to a collector 

 of Recent Mollusca this may not appear very conclusive, for quite 

 diverse faunas exist under present conditions on types of sediments 

 in which after induration the differences would probably not be par- 

 ticularly marked. 



The areal extent of the Upper Cretaceous sea is such as to suggest 

 that there was direct comrmmication between these two basins of 

 deposition. If this is a correct inference, isolation did not play an 

 important part in causing the faunal dissimilarities. 



The differences in environment, then, resolve themselves primarily 

 into the effects of temperature due to oceanic currents, and possibly 

 to differences of types of sediments. These all directly or indirectly 

 were affected by the distribution of land during this period. That 

 the shore line during the Upper Cretaceous was only a short distance 

 east of the present summit of the Santa Ana Range is inferred by the 

 type of sediments composing the Chico group of this region, and by 

 the absence of Chico strata at any considerable distance east of those 

 mountains. The Trabuco formation and the lower part of the Chico 

 have been described above as being decidedly conglomeratic, both 

 containing boulders apparently derived from rocks similar to those 



