PERMO-CARBONIFEROUS CONDITIONS AND TIME 501 
becoming increasingly evident to all workers in stratigraphy as 
well as paleobiology, fossils must be regarded and interpreted as 
once living things, and the problem of their distribution is inextri- 
cably associated with the problem of their living conditions. The 
method of evolution is as yet undetermined, but all biologists con- 
cede the directive influence of environment when a line is once 
started, by whatever means it was originated. In other words, 
evolution of life follows and responds to change, or evolution, in 
the inorganic environment. If this be true, the beginning of a new 
geological interval of time is marked by the change in the inorganic 
world which will lead by slow degrees and a multiplicity of processes 
to the development, or immigration into a definite area, of new forms 
of life. The new interval begins with the establishment of new con- 
ditions fitted for the new life and may precede by a very con- 
siderable period of time the establishment of the new life in such 
abundance as to be recognized as constituting a new fauna, faunule, 
or flora. On the other hand, it is very possible that the estab- 
lishment of new conditions may be almost immediately followed 
by the introduction of a new fauna or flora, as by immigration. 
These ideas are in strict consonance with the determination of 
geological intervals on the principle of diastrophism. 
_ If any progressive criteria can be detected and traced which 
reveal such a change in the inorganic world, then the evidence of 
the organic world may be better interpreted and even in some 
measure anticipated. Changes in the inorganic world are in gen- 
eral more obvious under terrestrial conditions than under marine, 
but a change from marine to terrestrial conditions would be the 
most obvious of all. 
The more evident and violent effects of diastrophism are readily 
detected and their results easily interpreted, but where the change 
is a slow and gentle one with slight disturbance of the rock layers 
and, as in a case of slow elevation, with a resultant destruction of 
the surface beds and sparse deposition of terrestrial sediments, the 
problem becomes far more intricate. In such a case it is some- 
times necessary to turn to more obscure and commonly neglected 
factors, such as the climatic alteration resulting from change of 
altitude and exposure of large areas of land. 
