6 
AMERICAN GEOLOGY. 
small eye would be of no use if the ground was lighted by fewer 
rays. The blind fish and the blind animals of the mammoth 
cave live in a period when the earth is lighted up most glori¬ 
ously: their abodes are dark, but yet the sun shines without 
in all its strength. We find, then, all conditions of the eye 
and the lungs at the present time. But it does not follow, that 
because the structure of the fossils of a given period may be 
found whose organs belong to a certain type, that the physical 
conditions of the earth were materially different from what 
they are now. This view of the subject does not conflict with 
the doctrine of adaptation, but rather sustains it. The physical 
conditions are first established; the organic kingdoms after¬ 
wards come in with their separate adaptations. The organisms 
are perfect in their adaption to the conditions in which they 
are to live, as well as to the position in space, and the mediums 
in which they are to be placed. The doctrine of progressive 
development, as usually represented, seems to be untrue. It 
proceeds on the ground that the earliest beings were the least 
perfect, and that progression consisted in the creation of those 
animals which were more perfect in their structures than their 
predecessors. But who can not see that the world is full of the 
same imperfections in animals now as in the beginning. Pro¬ 
gression has no reference to perfection of structure, but to rank. 
Structures have been always perfect, but rank has been pro¬ 
gressive. 
§ 7. Water acts upon the earth’s surface in many ways. It 
is a solvent. Temperature and pressure modify this property. 
Pressure and temperature combined increase it to an indefinite 
amount. It also acts mechanically. It permeates the solids 
and penetrates the fissures of rocks, and in the cold regions 
divides asunder the particles and masses in freezing. It is a 
carrier or transporter of the divided matter. Flowing in 
streams over the surface, it carries along from the higher to 
the lower levels the broken-down matter. When moving in 
masses, in the form of tides and waves of seas and oceans, it 
bears away and moves to distant points the mud and sand com- 
