377 
CROSBY : OKIGIN OF ESKERS. 
from its front or seaward margin undoubtedly have their sources 
high up in the valleys of the St. Elias range; and, as described by 
Russell (’93, p. 240) are seen in several instances to pass beneath 
the upper margin of this great piedmont glacier in well-formed, 
wide mouthed tunnels, the subglacial course of such a stream as the 
Fountain or Yahtse being merely an incident of its history. But 
the main point, of course, is that we have here more indubitably 
than anywhere else ice tunnels of considerable length—5 to 25 
miles at least — occupied by large and rapid streams, the outlets of 
which are being obstructed and raised by the deposition of coarse 
detritus swept out of the tunnels by the torrents or discharged by 
the slow process of ablation from the frontal slope of the ice, the 
conditions thus favoring the aggrading or building up of the beds of 
the subglacial streams by still coarser detritus which the deepening 
water could not urge to the outlet. In short, we appear to find here 
all the machinery usually regarded as essential to the subglacial 
'origin of eskers. 
But eskers are not a conspicuous feature of the land between the 
Malaspina glacier and the shore, across which the margin of the ice 
has recently receded — a tract which, though divided by the Sitkagi 
bluffs, aggregates nearly seventy miles in length. It is natural that 
it should be so, since, granting for the sake of the argument that 
ridge-like deposits of gravel may be formed in the earth-bottomed 
ice tunnels occupied by these impetuous subglacial streams, they 
must almost inevitably be obliterated or buried by the agency of the 
same streams, as fast as they are exposed by the recession of the 
retaining walls of ice and brought within the zone of extremely 
rapid fluvial deposition, where the overloaded streams are building 
their detrital cones. In fact, although scores of subglacial streams 
are escaping from the southern margin of the Malaspina glacier, 
Russell has noted on this marginal plain, several hundred square 
miles in area, but one esker, or distinct ridge of gravel, which is 
clearly the product of deposition and not of erosion. This is on the 
north side of and parallel with Kame stream, and is described as a 
sharp ridge of well-rounded gravel which is seen in places to rest on 
an icy bed and was evidently deposited by a stream which flowed 
fully one hundred feet higher (Russell, ’92, p. 180). Again, it is 
said to date from a former stage when the waters flowed about one 
hundred feet higher than now and deposited a long ridge of gravel 
