"FAUNAL RELATIONSHIPS OF THE MEGANOS GROUP'' 301 



In connection with this statement Clark refers to Weaver's 

 stratigraphic studies wherein Weaver shows that the Olequa and 

 ChehaHs of Arnold and Hannibal were reversed. Weaver's care- 

 ful work cleared up this succession but apparently does not invali- 

 date Arnold and Hannibal's assignment of the Arago as the upper- 

 most formation of the Eocene. Arnold and Hannibal regard the 

 type locality of Venericardia planicosta merriami, on Little River, 

 Roseburg Quadrangle, Oregon, as being in the uppermost portion of 

 the Eocene, their Arago formation, and in this general conclusion the 

 writer is in agreement. The evidence yielded by evolutionary forms 

 of Venericardia planicosta have not been sufficiently studied by 

 Dr. Clark. The first of these forms is V. planicosta venturaense 

 Waring and was described from the Martinez (Lower Eocene) of 

 the Simi Hills, Ventura County, California. Waring's type was 

 considerably eroded but a mature specimen collected from near the 

 type locality by the writer shows strong V-shaped ribs marked by 

 very prominent nodes. Now these characters are conspicuous only 

 in the youthful stages of V. planicosta hornii Gabb, the nodose 

 character disappearing rapidly as the specimen matures. In very 

 youthful specimens of V. planicosta merriami the same characters 

 appear but these forms upon reaching maturity are marked by 

 nearly complete obsolescence of ribs as well. 



Clark, in the writer's opinion, overemphasizes the presence of 

 new species in the Eocene and permits this to color his views. It 

 is the writer's experience that in California, where unusually good 

 preservation is found, many new species will be discovered. We 

 must not lose sight of the fact that the pelecypod and gastropod 

 fauna of the Tejon group is probably not much more than half- 

 described. And on this account we must not create new horizons, 

 based largely on such evidence. Again, let us not forget that the 

 Tejon group is largely composed of inshore or strictly littoral sedi- 

 ments, and that the lignite seams occurring commonly throughout 

 California, Oregon, and Washington, generally indicate deposition 

 in lakes or lagoons bordering the Eocene shore. Thus during the 

 deposition of the upper Tejon north of Mount Diablo three different 

 carbonaceous beds were laid down, and there is evidence to show 

 that the sea was at least temporarily withdrawn while these lignitic 



