6 University of Kansas Geological Survey. 
ment already existing in the ocean bottom produced layer upon layer 
of material over different parts of the ocean bottom which ultimately 
became changed into one kind or another of rock. 
As the contraction of the diameter of the earth continued, and 
probably is in progress even at the present time, the irregularities 
in the surface were correspondingly intensified. The valleys in 
the ocean bottom were made lower and lower and the valleys 
between the dry land uplands were likewise made more intense, so 
that the difference in elevation betwen the land areas and the water 
areas was constantly increasing. But the destructive agencies of 
the atmosphere were likewise active upon all the dry land as fast 
as it appeared above the ocean water and constantly larger quan- 
tities of sediment were carried from the dry land back into the 
ocean. In this way the superficial portions of the globe were con- 
stantly being worked over and spread out over the ecean bottom 
in the form of relatively thin coverings of stratified rock in which 
layer upon layer of first one kind of material and then another was 
produced. 
At the present time the greater portion of all of the dry land of 
the globe is covered with stratified rocks thus produced. The re- 
maining part is covered with rocks resulting from one form or 
another of volcanic action or, in rare cases, possible of a portion of 
the original dry land materials is preserved. 
The stratified rock, therefore, should be looked upon as relatively 
thin layers of sediments that have been accumulated and which have 
as great diversity of character as corresponds with the /different 
conditions under which they were formed. Some of them are com- 
posed principally of grains of sand weakly or strongly cemented 
together, producing the different kinds of sandstone. Others are 
products of the finer sediments, the material which was carried 
in such large quantities into the ocean from the dry lands. These 
are usually designated by the one term shale, with explanatory 
terms prefixed as occasion may require, such as clay, or argillaceous 
shales, sandy, or arenaceous shales, bituminous, or carbonaceous 
shales, etc. <A third kind of stratified rock which, is everywhere 
present is produced by the accumulation of the shells of the va- 
rious forms of marine invertebrates and is known by the general 
