TWO GLACIAL STAGES IN ALASKA 755 



extrusions of lava over the surface of till and outwash. The len- 

 ticular shape of the tillite beds may be due either to the shape of the 

 original morainal beds, or to local erosion following a time of ice 

 recession. The lack of induration of one thick till bed may have 

 been due to the impenetrability of the till itself, or of the underlying 

 shale, and is not believed to affect the general interpretation of the 

 section. The whole series of beds, with the exception of the lava 

 flows, is probably similar to the deposits now being laid down near 

 the terminus of many a glacier in this same mountain range. 



Little can now be said of the areal extent of the glacier which 

 left these old morainal deposits. The elevation of the present 

 exposures is of little importance, for the beds show by their struc- 

 ture that they have been tilted, with minor folding, and their present 

 elevation may be much different from that at which they were laid 

 down. At present the 3 ,000 feet of the beds described are seen with- 

 in a vertical range of only 1,150 feet. The beds at this locality 

 dip from 55° to 60° to the east, but the dips gradually become less 

 as the distance from the mountains increases, and as seen in the 

 canyon of North Fork of White River the tillite is nearly flat-lying. 

 All the known outcrops of tillite lie well within the limits reached 

 by the ice during its last great advance, and no comparison can yet 

 be made of the extent of the ice fields during the two stages. 



Summary. — -There have now, for the first time, been found in 

 Alaska deposits of glacial till which can be proved to antedate 

 by a considerable period of time the last great ice expansion, thus 

 proving that there have been at least two distinct glacial stages 

 in that territory. The deposits comprise a series having a thickness 

 over 3,000 feet and consist of indurated as well as unconsolidated 

 glacial till sheets, separated by outwash gravels and some assorted 

 sediments, and interrupted by lava flows. The section examined 

 was evidently deposited near the border of an oscillating ice edge 

 and shows ten definite advances of unknown magnitude, represented 

 by the deposition of till beds, followed by periods of retreat during 

 which water-laid beds were deposited upon the successive till beds. 

 After its deposition this series of glacial and glacio-fluvial beds was 

 covered by lava flows, at least locally, was uplifted, in part in- 

 durated, and was later deeply cut by erosion. A much later ice 



