836 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



as common in the Nushagak beds of Spurr, make me doubt their Tertiary age. I 

 beheve they must be younger." 



O-P 9. DBASE AND UPPER LIARD RIVERS, BRITISH COLUMBIA. 



Dawson/^*'' in a report on explorations in the Yukon district, describes a wide 

 plateau cut on Tertiary rocks, which are unconformable to the underlying Paleozoic 

 rocks. 



Q 5-6. YUKON VALLEY. 



Spurr ^^"^ distinguished two occurrences of Tertiary strata in the Yukon 

 Valley — one as the Twelvemile beds and the other as the Palisade conglomerate. 

 According to Brooks the former is now regarded as of Kenai (Eocene) age. Con- 

 cerning the latter Spurr says : 



On the left bank of the Yukon, about 35 miles below the mouth of the Tanana, cliffs of silt 

 and gravel rise to a height of 150 feet. This locality has been named the Palisades, but on 

 account of the occurrence in the silt of abundant bones of the mammoth and other large animals 

 it is more popularly known as the "Boneyard." The silts also contain lignite beds and small 

 land and fresh-water shells and are of Pleistocene age. About a mile below the beginning of 

 the silt bluffs the height of the vertical exposure changes from 150 to 200 feet, the increase 

 being apparently caused by a fault which is visible in the face of the bluffs and which upthrusts 

 the down-river portion. The fault is a normal one, and the silts of the upstream side are seen 

 to be upturned against the fault plane. On the downstream side of the fault there is brought 

 up a lower and more consolidated bed which underlies the silts. This new bed is pure white, 

 being composed of clean sand and well-washed pebbles. It is strongly cross-bedded and 

 contains much woody matter — sticks, logs, etc. — in a condition between wood and lignite. 

 Many of these woody layers are steeply inchned, being cross-bedded with the sandstone. This 

 bed is very gently arched and has a barely perceptible dip downstream. It is partly indurated, 

 so that while it yields with comparative ease to a pick, it is firm enough to stand in sohd, 

 nearly perpendicular chffs and falls in great slabs. 



In the materials collected from the woody layers Dr. Knowlton found fragments of dicoty- 

 ledons, but none sufficiently distinct for identification. Many of the layers are fuU of finely 

 preserved cones, which, according to Dr. Knowlton, appear to be the same as Heer's Pinus 

 macclurii, and from these he infers that the age is Pliocene, or possibly Upper Miocene. 



Q, 7. UPPER YUKON. 



Brooks'"'*" states: 



No beds have been identified on the Yukon which are positively known to belong to the 

 Pliocene or Miocene. It seems probable, however, that some terrace deposits may be of late 

 Tertiary age. Such interpretation of the facts in hand has been made by both- Spurr and 

 CoUier. 



McConnell ^°' thus describes the occurrence east of the international boundary : 



Beds referred to the Tertiary occur at several points around the outskirts of the gold 

 district. A wide band follows the Yukon Valley above Dawson, on the northeast side, and 

 continues on in a direction a little south of east to the Klondike, which it crosses a short distance 

 above the mouth of Rock Creek. It then follows the Klondike River to the mouth of Flat 

 Creek and probably underlies the belt of plateau country that borders the latter and extends 

 through to the Stewart. 



Exposures of these beds on Rock Creek and the Klondike River consist mostly of soft 

 grayish sandstones, indurated clays and shales, and occasional beds of ironstone. A thick 

 lignite seam is reported to outcrop on one of the branches of Rock Creek, and other seams occur 



