3o8 CALIFORNIA ACADEMY OF SCIENCES. 



Lawson, by whom they were called the Merced series.* 

 They have been called Pliocene by all who have worked 

 with them. From Half Moon Bay southward, at a num- 

 ber of places, occur very fossiliferous beds, which have 

 often been mentioned or referred to, but of which little 

 has been written. The fossils obtained from these beds 

 have been referred by some to the Miocene, by some to 

 the Pliocene. The same beds have been referred to the 

 Pliocene where little disturbed, and to the Miocene where 

 much disturbed. 



The field work done by the writer has seemed to show: 



1. That, though minor oscillations have occurred, 

 there has been continuous sedimentation from the begin- 

 ning of the Monterey series to the end of the Merced. 

 (Due to minor oscillations, this is not always true locally.) 



2. That the two are similar in structure, that structure 

 having been received from the movement which took place 

 at the end of the Merced period. 



3. That the fossiliferous beds south of Half Moon Bay 

 are conformable with the Monterey series below them 

 and the Merced series above them. 



4. That the Monterey series is Miocene, the Merced 

 series on Seven-Mile Beach principally Pliocene, and 

 the fossiliferous beds transitional between the two, con- 

 taining a mixture of Miocene and Pliocene forms. That 

 means that if a line were drawn between the Miocene and 

 Pliocene it would not come at the top of the Monterey 

 series, as usually defined, but from one to several hun- 

 dred feet higher, somewhere in the period of the fossil- 

 iferous beds. 



It would be difficult, if not impossible, to draw the line 

 between the two ages, as it would be largely governed by 

 individual inclinations. Accordingly the writer prefers 



^ Univ. of Cal., Bull. Dept. of Geol., vol. i, p. 143. 



