Correspondendence. 277 
creases slowly and gradually from the sides to a point near the center. 
A glance at professor Reid's map of the ice front, opposite page 55 of 
his paper in the National Geographical Magazine, will show more clearly 
than any words the relation which the space not crossed, between his flags 
Nos. 6 and 7, bears to the space which was crossed. Flags Nos, 5, 6, 7 
and 8 are all out in the swiftly moving part of the glacier. Had a flag 
been planted midway between Nos. 6 and 7 it is a perfectly safe predic- 
tion that no motion more rapid than 10 feet a day could have been dis- 
closed. Anything measurably greater than this, moreover, would result 
in a differential motion whose results on the ice would be almost incon- 
ceivable. One must have been out in the midst of that chaos of pinna- 
cles, sharp ridges and yawning crevasses, to fully realize the force of 
the foregoing statements. 
A study of professor Wright's map (Ice Age in N. A., p. 49) will show 
that his claim that professor Reid and he measured different portions of 
the glacier, is. founded on a misapprehension. Reid names 500 yards as 
the distance not covered by his flags. Professor Wright's points num- 
bered 2 and 5 cannot both lie in this space, as his figures (given on p, 50, 
Ice Age in N.A.) show them to be considerably over 3,000 feet apart, and 
though their direction does not correspond with the line of Reid's flags, 
their distance as projected on this line would be far more than 500 yards. 
But he states that point 3 moved 65 feet, point 5, 70 feet a day. One or 
the other, possibly both of these points, lies in ice in which professor 
Reid found a motion of 7.3 feet as a maximum. 
Further, professor Wright's measurements, taken by themselves, will 
not bear close scrutiny-. He maps a point. No. 4, about midway between 
Nos. 3 and 5. To this he assigns a motion of 36 feet a day, while points 
2 and 5, about equally distant from it to the right and left, are marching 
forward with a motion double this. Moreover, points 6 and 7, which are 
much nearer on a line with point 5 than point 4 is, are only moving nine 
and ten feCt respectively. Further, there is no means of telling which 
one of these points occupies the space which professor Reid's measure- 
ments did not cover, or whether any of them do. The directions of mo- 
tion, as mapped by professor Wright, do not coincide with the directions 
of the moraines. Muir glacier is retreating, hence it is undoubted that 
its motion was less rapid in 1890 than in 1886. But it strains the imagi- 
nation to an unwarrantable extent to ask credence for the proposition 
that the glacier was moving seven or eight times more rapidly in 1886 
than it was in 1890. A decrease of speed of even one-half in that time 
would be almost beyond belief. 
Professor Wright's method of determining the motion was by sighting 
on pinnacles, which he believed he could recognize from day to day. 
It was the only method open to him with the appliances he had, and with 
a party numerically so weak. Only a large parly, well equipped, and 
with a leader experienced in climbing over broken ice, can hope to set 
out flags across Muir glacier. The members of the party of 1890 were 
unable to distinguish pinnacles from day to day. Even with the flags 
to help them they considered it unsafe to trust to a pinnacle in order to 
