206 University of California Publications in Geology [Vol. 7 



that in a section 4280 feet thick the Monterey shale type occurs 

 within 400 feet of the bottom, and within 1800 feet of the top, 

 and also in the middle part of the section, and that when it 

 recurs its fauna recurs, we have a key to the proper understand- 

 ing of the Monterey series. The shale with its fauna may occur 

 practically at any part of the series, if the conditions of depo- 

 sition (and therefore of faunal environment) are favorable. It 

 does not correspond to a faunal time zone, except to the general 

 zone of the Monterey series deep water fauna. Its relationship 

 to shallow water faunal zones can only be determined if it con- 

 tains frequent intercalations of fossiliferous littoral sands. The 

 faunas generally published as of the "Monterey shale" strati- 

 graphic formation are mixtures of the Monterey Series "shale 

 fauna" and that of occasional littoral sands from the upper part 

 of the series. As example, it may be noted that the faunal list 

 just referred to as given by Haehl and Arnold for the Monterey 

 .shale contains all the forms given by Merriain for the "shale 

 fauna" and found apparently in the "Vaquero" zone as well 

 as in the upper part of the series. It merely happens that in 

 the areas studied by Fairbanks, Haehl and Arnold, the lower 

 part of the series is chiefly sand (or conglomerate), and there- 

 fore does not carry the "shale" fauna, and that after the shale 

 appears it shows no more fossiliferous sands to the top of the 

 series — so that the "Vaquero" fauna is not found intercalated 

 in the supposed later fauna. 



Faunal Zones. — That the littoral deposits of the series do show 

 faunal zones is brought out by Merriam in the paper just referred 

 to. "The upper division has its nearest affinities with the San 

 Pablo, from which it can be distinguished by the presence of 

 Clypeaster (?) brewerianus, Trochita costellata, several new 

 species of Modiola and other forms." "The fauna of the lower 

 division is much more characteristic than the upper : that is to 

 say, it differs more decidedly from that of the beds immediately 

 above and below it" (p. 378). He gives a faunal list and pro- 

 poses that it be called the zone of Agasoma gravida. 



Turning then to a general discussion of the formations in 

 the southern portion of the State, he concludes that the Agasoma 

 zone is widely developed and suggests that it may be divisible 



