184 GRAVEL AND PLACER MINING IN ALASKA. [bull. 263. 
which A', L, K, J is a part of cross section, it would not be possible 
to dredge beyond the point L in the direction of IV without having" to 
dig tailings in section IV, A', M, N. If the material in the triangular 
section is assumed to be loose and to stand at an angle of 45°, angle 
A', L, IV, the undredged ground in section PV, L, A' would be lost. 
At first the relative merits in the use of a pivotal spud or a headline 
were considered almost wholly from the standpoint of actual excava- 
tion, and the difficulties of disposing of the tailings did not receive 
nearly the attention their importance demanded. In the opinion of 
the writer the pivotal spud should be used only by dredges of the 
double and single lift type whose sluices are sustained by auxiliary 
scows. Several dredges of these types in Montana, having broken a 
number of pivotal spuds while dredging a tenacious material, have 
substituted a system of rope anchorages which does not recommend 
itself to the writer, as it appears better to make use of stronger spuds. 
The rigging consists of four wire ropes leading- from a high frame at 
the stern to anchors ashore. The pivotal spud appears to be more 
effective in holding- the dredge wjien excavating- indurated material 
and prevents its surging and ramming the bank. Attempt has been 
made to prevent this movement in headline dredges by placing the 
buckets closer together and thus bringing about greater continuity of 
contact between the buckets and the dredging surface. This, how- 
ever, has not been entirely successful. It is possible that the intro- 
duction of a number of rollers on the lower side of the bucket ladder 
and behind the lower tumbler would result in holding several buckets 
firmly against the material being excavated and prevent surging, as 
it is probable that this movement, in digging hard material, is caused 
by the alternate taking hold and letting go of the buckets, as only one 
bucket at a time is held firmly by the lower tumbler. The buckets 
behind the lower tumbler dig by their weight only, Avhich is insuf- 
ficient to force them into hard material. The use of some such device 
as above suggested, if successful, would probably make it possible for 
a headline dredge to excavate indurated material with the very impor- 
tant advantages of mobility and the better distribution of tailings. 
The use of lower tumblers of more numerous faces causes more 
buckets to dig at a time and results in less surging. It is possible 
that the use of a round tumbler of large diameter might entirely elim- 
inate the surging, for there would then be no raising and lowering of 
the buckets as there is during the revolution of the tumbler of few 
faces. 
The use of the pivotal spud introduces a number of problems in the 
disposition of tailings. The spud should be so located as to make the 
radius of the arc described by the buckets in digging as long as possi- 
ble, thus permitting the excavation of a wide cut — an obvious advan- 
tage. This demands the placing of the spud at or near the stern. The 
