300 ROY E. DICKERSON 



discussion of these essential matters. Clark has evidently missed 

 the significance of this evidence as he states on page 162 of his 

 paper that 



Dickerson attempted to establish the stratigraphic sequence of his upper 

 faunal zone in relation to that of the typical Tejon indirectly, not having the 

 two faunas in the same section. His idea that the Siphonalia sutterensis 

 fauna is younger than that of the typical Tejon appears to have been founded 

 principally upon what he considered evidence for different stages of evolution 

 of certain pelcypods, such as Venericardia planicosta merriami Dickerson and 

 Cardium marysvillensis Dickerson. He believed that the variety merriami 

 was derived from the variety hornii Later stratigraphic work has shown that 

 these species occur in a sequence the reverse of that which Dickerson originally 

 supposed, the Venericardia planicosta merriami coming in beds older than those 

 containing the variety hornii. The same is true of the other species, which were 

 derived from typical Tejon species. 



It is true, however, that the problem of lone-Tejon relations was 

 attacked with faunal weapons as well. Clark states that "Later 

 stratigraphic work has shown that these species occur in a sequence 



the reverse of that which Dickerson originally supposed " 



In the historical review on page 129, Dr. Clark reviews a short 

 paper, by Arnold and Hannibal, and includes the following quota- 

 tion from it: 



The writers have shown that in Oregon and Washington the Eocene may 

 be divided into three faunal divisions, the Chehalis, Olequa, and Arago or 

 lone formations. The Chehalis formation is characterized especially by 

 Venericardia hornii Gabb, Meretrix calif ornica, Pecten (Chlamys) landesi or 

 Venericardia hornii Gabb and a tropical flora, and the Arago or lone formation 

 by Turritella merriami Dickerson, a form of V. hornii with obsolete ribs (var. 

 aragonia A. and H.), and a tropical flora. 



The Arago or lone beds represent a horizon younger than any Tejon 

 recognized in the Tejon or Puget Basin. The Arago or lone beds occurring 

 as they do in basins distinct from those in which the Tejon series is developed, 

 and being formed at a different period, must be treated as a distinct division of 

 the Eocene. 



' Arnold and Hannibal use formation as an equivalent for faunal zone or horizon 

 and loosely use formation, group, series. The form referred to as V. hornii var. aragonia 

 A. and H. was not described by them but was collected at the type locality of V. 

 planicosta merriami, on Little River, Roseburg Quadrangle, Oregon. Arnold and 

 Hannibal classed these beds as Arago (or lone). 



