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IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
the very nature of things the young earth probably had arid 
regions and periods as well as humid ones. 
Probably it was not long after this that volcanic action began 
on the growing earth. With the continual infall of material there 
was a parallel tendency to readjustment, reassortment, and con- 
sequent condensation. This would cause increased pressure and 
pressure generates heat. The heat at the center moved outward 
into regions of lower pressure and here the melting points of 
some substances were reached. The tendency was for these fused 
masses to ascend and hence in time the surface was reached. In 
many cases the lava so formed cooled as great masses within the 
porous outer zone. In other cases it welled quietly out upon the 
surface, and in yet others, where gases were confined within the 
molten rock, violently explosive eruptions took place. The climax 
of vulcanism seems to have been reached during Archean time, 
at the very beginning of observable geologic history. Since then 
the processes of weathering, erosion and sedimentation have be- 
come more and more predominant, although there have been re- 
peated outbursts of volcanic activity such as those which gave 
us the trap rocks and granites of New England and the great lava 
flows of the Columbia river basin. But most of the post- Archean 
rocks are sedimentary deposit^Tormed by the agency of wind and 
water. 
It is probable that radio-activity was a contributing factor in 
initiating and perpetuating volcanic activity, just as electricity 
and magnetism were influential in helping on the growth of the 
earth knot. 
It was inevitable that there should be irregularities in the 
surface of the young sphere, both from the infall of planetesimals 
and from volcanic activity and deformative movements. In the 
hollows thus formed the hydrosphere first appeared at the sur- 
face. As more and more water-vapor condensed and the hydro- 
sphere grew the lakelets increased in size and numbers until the 
.oceans of today were developed. The material which underlay 
these water bodies and which fell into them was less subject to 
weathering processes than the material which formed the land 
areas and as a result the land masses' came to have a lower 
specific gravity than the suboceanic masses. This resulted in pro- 
gressive compression and depression of the ocean basin and cor- 
responding laying bare and crowding of the land masses. Crump- 
