292 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
TRICKLE PATTERN IN CLAY. The experiment last described was 
coarse. The model was bulky and very laboriously made. ‘The 
coarse sand layers were made of material the equivalent of gravel in 
proportion to the size of the streams developed. Hence it seemed 
desirable, if in any way possible, to work with finer material, so as 
to reduce the scale of the phenomena studied and likewise diminish 
the labor by making less bulky models. Plate 4 shows a pattern 
developed in liquid modelling clay. The phenomenon is closely 
analogous to the trickle of raindrops on a windowpane. A glass 
plate 15 X 20 inches (.38 X .50 m) rectangular, was flooded with 
smooth liquid clay of the consistency of syrup. The clay was 
“flowed” over the surface, held horizontally until it was evenly ‘cov- 
ered. The plate was then allowed to rest on one of its lónger edges 
and raised until the surface dipped 45 degrees. It was supported in 
this position and left to drain. The greater part of the clay ran off 
and formed a pool at the lower edge of the plate. A portion, however, 
clung to the glass, settled, and its water tended to separate.and run 
down the slope in drops, making clear spaces along the streams and 
leaving the divides opaque. Plate 4 is a portion of the upper margin 
of the plate, printed after it was dry by direct contact with solar paper. 
(The right and left are therefore reversed). For a width of five inches 
(.127 m) the upper margin showed an arborescent tracery on so fine 
a scale that from 20 to 25 streams are crossed in a distance of 7 
inches (.178 m) (Plate 4). Lower down the slope distributary phe- 
nomena interfere with the arborescence, and the pattern is a complex 
of streaks with V-shaped accumulations of clay pointing up the slope. 
A number of experiments were made with this process. In one 
series of plates, made under similar conditions, the duration of drain- 
ing was systematically varied, so as to show all stages from the first 
initiation of arborescence to its completion. After the first sheet- 
flood run-off, the arborescence always develops near the upper margin 
of the plate in a definite zone about two inches from the margin. It 
seems to develop all at once and to grow very little thereafter. This 
is to be expected, as there is no source of added water, and nothing to 
erode when the glass is reached. There is interference of adjacent 
streams in many places, but the control of initial drainage basins and 
of “shadow” are clearly shown. The trickle pattern is complicated 
with capillarity and much of it is mere drop-trickling. It shows, how- 
ever, that the tendency to digitation may be studied on a very small 
scale, and these experiments led to an effort to produce something 
intermediate between these too quickly drained clay films and the 
