156 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
have persisted from the past. The bizarre, the ultra-radical as 
well as the ultra-conservative, have disappeared, or, what is .just 
as fatal to real progress, have failed to keep pace with the march 
of the race, have fallen hopelessly behind in the onward sweep 
of life toward higher and higher development. 
The trend of modern scientific thought has been away from the 
cataclysmic toward a more uniformitarian point of view. We 
are coming to understand that present forms of life differ from 
those existent during earlier periods not because they belong to 
a distinct creation but because they have progressed during the 
ages, have developed those traits and characters which fitted 
them to compete with untoward conditions and unfavoring cir- 
cumstances. 
If we turn to inanimate nature the same rule of uniformity 
holds good. The rock foundations of the continent to the :pro- 
foundest depths yet penetrated bear every evidence of formation 
by the same agencies and under control of the same laws as 
those now operative. The only differences are those of location 
and degree. There was a time when, according to the most 
modern and reasonable theory of earth history, the upbuilding 
of the earth’s mass by accretion from outside sources was the 
dominant activity. At other and successive periods volcanic 
forces have raged with tremendous violence and enormous vol- 
umes of liquid rock have poured over the surface or have been 
thrust into the solid body of the earth. During still other pe- 
riods, and these have been the dominant ones of the earth’s later 
history, the quiet processes of erosion of the lands and deposition 
in the seas have been uppermost in importance. These latter 
processes have given us our sandstones, the beds of shale which 
enclose our coals and the limestones which form such an impor- 
tant resource for constructional purposes. To them we owe in 
large measure our vast resources of iron, of rock salt, of gypsum 
and of other minerals. And these processes are today as active 
as ever they were. The mud banks and sand bars at the mouths 
of our great rivers, the limy clays and beds of shell and coral in 
the quiet, shallow off-shore reaches of the modern oceans, these 
will as surely consolidate into solid rock as have similar deposits 
of the past. 
It is my purpose to outline briefly the progress of the ideas 
which have been held successively by students of natural his- 
