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



29 



imately twenty degrees. In all of the localities in which the 

 mammal beds of Thousand Creek have been observed they are 

 nearly horizontal. Though no observations have been made at 

 their actual contact with the older formation, there would seem 

 to be a strong angular unconformity between the two. 



Whether the sedimentary beds in the upper portion of the 

 Pueblo Range section actually belong with the lavas and tuffs 

 below is not certain. They, with the lavas, appear to represent 

 one general period of deposition. At all events they both 

 antedate the period of deformation which preceded the deposi- 

 tion of the Virgin Valley and Thousand Creek beds. 



For practical purposes it is desirable to refer to the rhyolites 

 and basalts on the western side of the Pueblo Range, with 

 whatever eruptives or other beds may be shown to belong in the 

 same series, as the Pueblo Range Series, a geographic designation 

 indicating the section first described by Blake. This section 

 is geographically so situated that it should be possible to 

 correlate it with other igneous series in the region of southern 

 Oregon and northern Nevada. To this series the Canon Rhyolite 

 bordering Virgin Valley apparently belongs, although it is not 

 entirely certain whether it represents exactly the same horizon 

 as the rhyolites exposed in the upper part of the section 

 immediately to the west of Mud Lakes. A careful study may 

 show the Pueblo Range Series to be composed of several fairly 

 distinct divisions. 



PINE FOREST RANGE. 



Corresponding in a manner to the observations of Blake on 

 the Pueblo Range, the work of the University of California 

 expedition has shown that the prominent mountain mass known 

 as the Pine Forest Range (pi. 2) which overlaps the southern 

 end of the Pueblo Range, comprises a granitic mass bordered by 

 rock series which have undergone considerable alteration in 

 many eases. On the eastern side of the southern end of the 

 range there are extensive exposures of limestone which appear 

 from a distance as a grayish band running obliquely up the 

 mountain slope from the south. In this exposure Miss Alexander 

 obtained a considerable number of specimens made up largely 



