224 



University of California Publications. 



| Geology 



clear understanding of the relation of the physical and biologic 

 successions to each other will often make possible the bringing 

 together in intelligible form of evidence otherwise entirely with- 

 out meaning. 



Relation of Virgin Valley Beds to the Middle Miocene Forma- 

 tions of tlw Pacific Coast and Basin Regions. — As has been set 

 forth in Part I of the present paper, 8 the Virgin Valley Beds 

 rest upon a floor of older igneous rocks, which apparently cor- 

 respond to the upper portion of a great series of basalts and 

 rhyolites to which the tentative name of Pueblo Range Series 

 has been applied. This igneous series has been traced to the 

 north by Waring, 9 and is considered by him to represent a south- 

 ward extension of the great lava flows along the Columbia River. 

 The complete section from southern Oregon to the typical region 

 of the Columbia Lava has not been actually traced, and it is most 

 desirable that the connection should be carefully worked out. 

 There are, nevertheless, strong reasons for considering with Blake 

 and Waring that the eruptive series of southern Oregon is only 

 a part of the series of flows which cover such an enormous extent 

 of territory farther to the north, and certain suggestions as to 

 broader correlations may tentatively be based upon this suppo- 

 sition. 



It is well worth noting that the relation of the Virgin Valley 

 Beds to the older rocks referred to the Pueblo Range Series as. 

 determined on purely physical evidence is approximately the 

 same as the relation of the Mascall Beds of the John Day region 

 to the Columbia Lava ; while on the basis of the similarity of 

 mammalian faunas the Mascall and Virgin Valley are considered 

 as representing the same epoch, viz., the Middle Miocene. The 

 biological and physical relations considered together seem to indi- 

 cate pretty clearly that we are dealing with the same stratigraphic 

 sequence in the two regions. 



The relation between the Columbia Lava and the Middle 

 Miocene sedimentary formations containing a characteristic 

 mammalian fauna seems to be one of unusual importance for 



s Univ. Calif. Publ. Bull. Dept. Geol., vol. 6, pp. 26-30, 1910. 

 "Waring, G. A., U. S. Geol. Surv. Water Supply, 231, p. 2, 1909. 



