286 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
ments in the problem, however, which have been given less attention 
by geomorphologists:— initial catchment basins, and initial attitude 
of aquiferous strata. The whole surface of an uplifted sea-bottom, 
for example, does not immediately become covered with streams. 
Rivers are extended from the old land and a limited number of new 
tributaries and longshore streams develop, apportioned in number to 
the rainfall and to the underground water supply. Their loci and 
spacing are dependent first upon extremely faint irregularities divid- 
ing the surface into a few flat catchment areas. After some gorges 
are cut, strata relatively impermeable or water-bearing are opened, ) 
and underground reservoir areas take control. When this happens 
if there be the faintest possible longitudinal tilt to the beds, local or 
general, there will be unsymmetry in the development of subse- + 
quent branches. A flat syncline of deposition with axis normal to 
the shore line would give mastery to any stream, small or great, 
cutting into aquiferous strata along its axial line. A much greater 
stream from the old land might cut a deep gorge along the adjacent 
faint anticlinal axis. It would have no power to send young branch 
ravines “gnawing headward” right and left. The underground pores 
would tend rather to drain it than to feed it, if the river cut into a 
permeable stratum. Hence extremely slight initial surface slopes 
and the underground slopes of impermeable water-bottom strata 
must be taken into account in any argument which deals with river 
piracy, divide migration, and “consequent,” “subsequent,” or “obse- 
quent” streams. 
Imrrative CHARACTER or Rīts. The subject of drainage modi- 
fications is not without experimental possibilities. The delicate rill 
patterns seen on beaches are but one step removed from “bad-land” 
valleys; the latter again are analogous to all land drainage, when due 
allowance is made for the effects of geological structure. Such allow- | 
ance is too often neglected on the one hand, or imagined structural 
influence is too much accentuated on the other, as in those cases 
where river pattern is attributed indiscriminately to the influence of 
joints and faults, and residuals are believed, because of their saliency; 
to possess specially resistant rocks. 
Purrosk or ExPERIMENTS. The present study deals with a series 
of experiments designed to perfect apparatus for reproducing ril 
patterns in the laboratory. In the later of these experiments some 
success was attained, and meanders, piracy, digitation, corrasion, 
