370 The American Geologist. June, 1893 
sketch them so that Prof. Wright could recognize eacli one and 
call it by name. Prof. I. C.Russell writes me that in his attempt, 
in 1890, to measure the motion of the Seward glacier, his base line 
was on the same level as the boulders and pinnacles to which he 
sighted, and the identification was complete. 
In fact, a re-examination of the measurements shows no room 
for error more than the probable error necessar}^ to any observa- 
tions under such conditions. What this is cannot be exactly as- 
certained. Prof. E.eid gives as the possible error in his observa- 
tions two feet, or a ratio of 2:7. Prof. Wright's measurements 
were made with a less accurate instrument, but, on the other hand, 
the ratio of probable error decreases as the distance measured is 
greater, so that 2:7 would seem too large. That ratio would be 
twenty feet, but the probable error can hardl}' be more than ten 
feet, with a possible error of fifteen. 
B. Prof. Reid, finding it impossible to identify seracs from his 
base line, undertook to set a line of flags across, and measured 
their motion with a theodolite, from two points on opposite sides 
of the glacier.* 
Prof. Reid made only two observations on his most rapidl}- mov- 
ing flags, on July 21st and four da^'s later, but on the flags nearer 
the sides he was able to make several measurements. He gives 
two feet as the amount of possible error on his central flags. Thus 
it would seem that only a very small part of the discrepancy 
can be explained by inaccuracy of observation. 
2. Difference of Method or Locality. 
A. Prof. Reid, speaking of his inabilit}^ to find the direction of 
motion from his observations, says: "This, however, was unim- 
portant, for the direction is given by the moraines, which were 
about at right angles to the line E-K. " This seems not quite ac- 
curate, for examination of the map shows that the moraines of the 
eastern half are crowded h^ the strong stream from the north 
more and more toward the east side, as they near the front of the 
glacier, without anywhere turning toward that side. 
According to Prof. Reid's map, the moraine from Nunatak I, 
in moving two miles down the glacier, is forced three-fourths of a 
mile to the side. The moraines from Nunataks H and I, in mov- 
ing one and a half miles down, move five-eighths of a mile toward 
*Nat. Geog. Magazine, vol. iv, p. 43. 
