Vol. 6] Merriam: Virgin Valley and Thousand Creek. 



33 



As extensive lava formations both older and younger than the 

 Columbia Lava are well known in the great Columbia River 

 area immediately to the north, it is desirable that the eruptive 

 series of southern Oregon should be carefully compared with 

 those of several typical sections where the age and relationships of 

 the lavas have been determined. From the point of view of 

 general geology it is very desirable that an attempt be made to 

 connect the area mapped in southern Oregon with the section 

 of the John Day region, which is the most satisfactory series 

 of formations for correlation purposes that has yet been observed 

 in this region. 



"With our present knowledge of the eruptive formations of 

 southern Oregon, there is reason for considering the principal 

 lava series, of which the Pueblo Range Series seems to be repre- 

 sentative, as presumably, though not certainly, the correlative of 

 the definite horizon of eruptives situated between the John Day 

 and Mascall formations on the John Day River, at Picture Gorge, 

 near Dayville, Oregon. To this phase of the igneous succession 

 the name Columbia Lava has been definitely limited by the 

 writer 10 , as it seemed desirable not to discard entirely the name 

 so appropriately suggested by Russell" for the great lava flows 

 of the Columbia River region 12 . 



Virgin Valley Beds. — Resting upon the Canon Rhyolite in 

 Virgin Valley is a thick sedimentary series, consisting largely 

 of volcanic ash and tuff, which has been designated as the 

 Virgin Valley Beds 13 (see pi. 5; and text fig. 2, p. 30). It is 

 from this formation that the Tertiary mammalian fauna of 

 Virgin Valley is obtained. 



The Virgin Valley Beds have been protected by the over- 

 lying Mesa Basalt, which now forms extensive table lands on 

 each side of the valley ; and in the escarpments bordering the 

 mesas exceptionally good sections are exposed. Although a con- 

 siderable fauna has been obtained from these beds, vertebrate 

 remains are nowhere abundant in them, and the collections 

 available represent much painstaking effort. 



to Univ. Calif. Publ. Bull. Dept. Geol., 2, p. 303. 1901. 

 " Russell, I. C, U. S. Geol. Surv. Bull. no. 108, p. 20. 1893. 



12 This igneous series has also been known as the Columbia River Lava. 



13 Merriam, J. C, Science, n.s., 26, 1907, p. 380. 



