144 R. Pumpelly—Secular Rock-disintegration. 
the range of a fauna peculiar toa given coast is more limited 
than the area affected by the silt. The waters of the China 
sea for one hundred miles or more out to sea are yellow at the 
surface with loess-mud along six hundred miles of coast; and 
when we consider the extreme slowness of deposition of this 
fine material, we cannot doubt that below the surface the silt 
extends eastward to the Kurosiwa, and follows the lower strata 
of this current far to the northeast. 
is rapid transfer will, sooner or later, bring all the loess 
into the ocean, and thenceforth the waters of the streams and 
the coast will be clear, or alternately clear and turbid, in pro- 
“a ig to the absence or frequence of oscillations of the coast 
evel. 
Environment and plasticity have been described as interreg- 
nant directing forces in evolution. It is during this peri 
of turbid waters that the influence of environment and plastic: 
ity must be the most important factors in the evolution of life- 
forms; usurping, for a greater or less length of time, the post 
tion held for long ages by the purely biological factors—survi- 
val of the fittest, and heredity. 
temporarily become sufficiently extreme to destroy the veget 
tion, while a general glacial action presupposes a very moist 
climate. 
