Geology and Mineralogy. 399 



cupied by smooth, round gravel. Where the gravel does not appear 

 it has either been removed by erosion or is covered by later lavas 

 or else was not originally deposited, as in the case of the islands. 

 The gravel as now exposed, ranges in thickness from a few feet to 

 over 400 feet. The pebbles of the older portion are of the aurifer- 

 ous slate series including old eruptive rocks, but the upper portion 

 in many places especially along the beaches about the islands is 

 composed largely pf andesites and other later eruptives. Three 

 islands of lava, chiefly volcanic breccia, have been noted ; these 

 are surrounded by beaches which in some cases are very well 

 marked and not to be misunderstood. It is possible and even 

 probable that the older gravels extend beneath the volcanic 

 islands for the older gravels and the breccia are like those of the 

 gravel channels farther south. At one point a dike is found in 

 the gravels of which a large mass has been cemented so as to 

 form conglomerate. In the Susanville region the gravels run 

 beneath the Lahontan beds so they are of greater antiquity. 



Originally the range in altitude of the gravels could not have 

 exceeded a few hundred feet, but now they range from 4200 ft. on 

 Gold Run to 7400 on the crest east of Diamond Peak a difference 

 of 3200 feet. This difference as I have previously maintained 

 (8th Annual Report) is due to displacement along the eastern 

 escarpment of the Sierra Nevada. From the lower part of Gold 

 Run near Susanville the smooth treeless gravel ridges and beaches 

 on the crest of the range 3200 feet above, near Diamond Peak, are 

 conspicuous. In the valley of Gold Run it is easy to distinguish 

 between the gravel of that stream and the original lacustral 

 deposits and the latter can be traced continuously from Diamond 

 peak or mountain to near Susanville. The fault along Honey Lake 

 runs out in an arch along Gold Run, and the Sierra Nevada ends 

 to be succeeded by the volcanic cones of the Lassen Peak region. 



I have already referred to the conglomerate cut by eruptives. 

 It is at the head of Cheney Creek where the " conglomerate 

 gravels " are bent down over the eastern slope. Gold Run fol- 

 lows close to the contact between the conglomerate and underly- 

 ing diorite (or granite) ; the principal rock of that portion of the 

 Sierra Nevada. That the conglomerate is only cemented aurifer- 

 ous gravel is shown by the fact that it grades into the gravel 

 away from the particular eruptive which penetrates the mass. 

 The pebbles and all features excepting degree of lithifaction are 

 the same. The plants in both are essentially of the same age and 

 in some cases identical species as determined by Ward and Les- 

 quereux. The feature to which I wish in this connection to call 

 attention is that where the fault runs into the arch and the con- 

 glomerate is bent over the eastern slope the pebbles are in many 

 cases fractured and faulted. The argument in favor of displace- 

 ment since the auriferous gravel period appears strong and con- 

 clusive. 



3. A Subtropical Miocene fauna in Arctic Siberia. — Dr. W. 

 H. Dall, of the Smithsonian Institution, has given an interest- 



