University of California. 



[Vol. i. 



are marine shells, among which the following 

 v species were identified for me by Dr. Dall: — 

 ur> Crepidula praerupta. 



2 Nassa mendica. 



Nassa prob. californiana Conr. 



Pleurotoma (spec, indet.) 

 g Olivella prob. biplicata. 



E Cardium (fragment). 



Bittium filosum Glcl. 



jo Upon such palaeontological evidence rests 



™ the determination of the Merced series as of 

 Pliocene age. The stratigraphical observa- 

 tions of the writer are in harmony with this 

 determination. 



Thickness. — The Merced series, as exposed 

 in this very favorable cliff section, has been 

 subjected by the writer to systematic observa- 

 tions for strike and dip, with the object of ob- 

 taining data upon which to base an estimate of 

 its thickness. The observations were taken 

 along the base of the sea-cliff from Mussel 



£ Rock to Lake Merced. In deducing; the re- 

 re _ ° 



1-5 suits from the observed strikes and dips it was 



found convenient to divide the section into 



c a number of separate parts, in each of which 



"■a the strike and dip are sufficiently constant to 



c/3 give reliable averages. The sum of the thick- 



■■o ness of these parts is the total thickness of the 



| series. The results are given below. Should 



they seem incredible to any doubting geol- 



.5 ogist, the section is easily accessible from San 

 Q . . . 



Francisco, and the writer invites inspection of 



the section, as one of the most imposing and 



o 



Oh ~ 



u S 



3 o 

 Pi .2 

 o J 



o instructive that he has anywhere met with, 

 o 



