300 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
however, made no great headway in extending its new headwater 
basin, because it in turn was shadowed by the next side stream above. 
The latter controlled a broad portion of the accumulation zone, and 
being at no disadvantage as to fall, yielded nothing to E. Fig. 3 and 
Plate 6 show the final result. 
The other features of this model which deserve some notice are the 
symmetry of M (Fig. 3) in contrast to the unsymmetry of R. Mis: 
typical medial stream which has developed freely with a delicate 
pattern of arborescence. R has had its left bank shadowed by the 
left side-streams from the first inception of drainage. The left side- 
streams possessed an advantage in quicker fall to baselevel, conse- 
quently they appropriated the waters of the whole area to the left of R, 
and nothing was provided whereby R could develop left-bank tribu- 
taries. R was not so shadowed to the right, where it controlled the 
accumulation area A over the space between M and the left side- 
streams. Its right tributaries dominate the space between R and M 
in a fashion similar to that whereby the left side-streams control the 
space between the left edge of the model and R. Probably there was 
a faint initial slope from M left-ward in the original construction of 
the surface. R was not captured by the left side streams because it 
was enabled by a low baselevel to trench and maintain a divide on its 
left bank even though it could not gather water from a wide enough 
lateral area to develop important tributaries. 
Discussion or PrinciPLES. The foregoing experiments suggest 
many questions and answer few. . They are based on the assumption 
that the extraordinary similarity of the rill pattern to the mapped 
pattern of rivers is due to government in both cases by similar laws. 
The writer recognizes the fact that in drawing analogies, only the 
mechanism of falling, running, and seeping waters is imitated, and 
not the erosion mechanism resulting from degeneration, winds, vege- 
tation, rock-joints, and other phenomena which complicate the prob- 
lem in nature. He believes, nevertheless, that river, creek, brook, 
rill, spring, and underground water coöperate in an orderly system of 
land sculpturing related to structure. This system implies a mech- 
anism hydrostatic, corrasive, and depositive. Physical geography 
has produced valuable studies of form, and has classified forms in 
accordance with inferred processes of corrasion and deposition. But 
physical geography has neglected hydrostatics, and has not quantita- 
tively nor experimentally investigated the processes inferred. T his 
paper will have accomplished its purpose if it starts certain funda- 
