A CRITICISM OF THE "FAUNAL RELATIONSHIPS OF 

 THE MEGANOS GROUP" BY BRUCE L. CLARK 



ROY E. DICKERSON 

 Manila, Philippine Islands 



In a recent paper^ published in the Journal of Geology Dr. Bruce 

 L. Clark revises the Eocene scale of California by introducing a 

 new division, the Meganos group, by cutting off the lower portion 

 of the strata which had previously been referred to the lower 

 Tejon. Clark's essential basis for division is stratigraphy first 

 recognized in the area north of Mount Diablo, Contra Costa 

 County. After his recognition of an unconformity in this area, 

 subsequent faunal work led him to assert a marked faunal break 

 as well although he recognized that the fauna obtained from these 

 beds "appears to be more closely related to the Tejon than to the 

 Martinez." In this paper Clark deals with the general correlation 

 of the middle and upper Eocene Sections of the Pacific Coast and 

 he tentatively correlates his Meganos group with the Wilcox of 

 the Gulf Coast. 



Owing to his absence from the United States, the writer is 

 unable to discuss this paper in detail, but there are certain general 

 conclusions of Dr. Clark's to which he wishes to record a firm 

 dissent. 



The evaluation of an unconformity is frequently a difficult 

 matter and in many cases only a close study of the faunas from 

 above and below the line of unconformity will enable the paleon- 

 tologist to determine the relative value of the time break recorded 

 in the rocks. Now the recognition of the existence of unconformi- 

 ties within the Tejon Group is not new, and largely upon this 

 account the writer has consistently clung to the term group in 

 describing the Tejon as a stratigraphic and faunal unit. In 

 making a study of the Tejon Group, its probable future division 



' Bruce L. Clark, "The Stratigraphic and Faunal Relationships of the Meganos 

 Group, Middle Eocene of California," Jour. Geol., Vol. XXIX (1921), pp. 125-65. 



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