.MAMMOTH REMAINS OF NORTHERN REGIONS. L23 



according to Captain Charles Peterson, of the steamboat " Yukon ", is com- 

 posed of frozen " sand." The fact that the strata are frozen accounts for the 

 steepness of the escarpment. As the river washes away its hanks, large 

 numbers of bones, teeth, and tusks are exposed. I was in formed also by 

 Peterson that the deposit near the delta is of the same general character as 

 the one here described. 



The position of the strata forming the bluff at the Palisades, as well as 

 their regularity of stratification and fineness of material, indicates a lacustral 

 origin. What is known of their fossils suggests Pleistocene or Tertiary age. 



The banks of the Yukon in the lowlands above the Lower Ramparts, and 

 at many localities lower down stream, are formed of flood-plain deposits and 

 are much more recent than the high bluffs at the Palisades. From this, 

 together with what I learned concerning the occurrence of detached bones, 

 teeth, etc., at many places along the Lower Yukon, it seems very probable 

 that they were not in the original place of interment, but had been washed 

 out of the bluffs at the Palisades, or other similar deposits, and transported 

 down stream. Similar bones have been found above the Palisades, however, 

 and I suspect that other " bone beds " exist higher up the river. 



It is necessary to note that the statements just made do not seem to har- 

 monize with the observations of Dall and others, who found mammoth 

 remains in the earthy layer on top of the ice cliffs near Kotzebue sound. 

 The vertebrate fossils in the stratified beds at the Palisades certainly seem 

 to be older than the similar remains occurring on the surface of the tundra. 



Extinction of the Mammoth. — It is an interesting fact that all the bones of the 

 mammoth and of other large animals that have been found in Alaska occur, 

 so far as 1 am aware, in regions not glaciated during the Pleistocene period.* 

 The relation of mammoth remains to the distribution of glaciers in Alaska 

 acquires additional importance in view of the fact that no evidence of glacia- 

 tion has been reported in northern Siberia, where similar mammalian remains 

 are also abundant. 



The study of glacial records by various observers has shown that the great 

 Pleistocene glaciers of this continent extended outwards in all directions 

 from two main centers of accumulation, one in Labrador and the other in 

 the northern part of the Rocky Mountain region. During their greatest 

 extention these two great glacier systems seem to have been confluent, so 

 that a vast ice field stretched across the continent from ocean to ocean. 

 The northward movement of the ancient ice sheet was not 'sufficient in all 

 places to reach the Arctic ocean. In view of this fact, it may be suggested 

 that the abundance of mammalian hones in the nonglaciatc.l regions in the 

 far North is due to the crowding northward and final extinction of land 



**The absence of glaciers in central and northern Alaska is discussed elsewhere in this pitper. 

 XVII— BtftL. Geol. Soc. Am., Vet,. 1, I- 



