Introduction to Kansas Geology. 7 
term of limestone. Here likewise various explanatery terms are 
employed to specify in greater detail the particular character of 
the limestone. In this way the whole of the stratified rocks of the 
earth may be classed under the three general heads of sandstone, 
shale, and limestone. 
These various forms of material are interbedded with each other, 
sometimes in a very intricate manner, but usually in such forms 
that their relations to each other can be easily understood by those 
who are trained in field work in geology. The surface of the globe 
in any one particular place rarely exhibits more than one or two or 
pessibly three of the various forms of rock just described, but by 
traveling some distance in any direction others are usually reached 
which overlie or underlie the ones first examined. The different 
strata in this way are brought to the surface so that they can be ex- 
amined. Passing under each other in whatever direction is neces- 
sary fora particular place, the strata are found in positions some- 
what similar to the position occupied by the shingles on a roof. 
The time occupied in the formation of each of these stratified 
rocks has been very long, has included almost all the time gener- 
ally understood as geologic history. For convenience and sim- 
plicity of expression it is desirable to refer to the various time 
epochs during which different rock strata were being formed, and 
correspondingly refer to the rocks produced during such time epoch. 
In the history of the rise of the science of geology we find that 
different customs have been followed at different times and by 
different peopie, so that there has not been a perfect uniformity in 
the choosing of names for time periods or for rock formations. But 
as the science grows older this disparagement of usage will grad- 
ually grow less. In 1889 the United States Geological Survey! de- 
cided upon a certain series of names to be given to the great time 
periods, which in general correspond with the usages of standard 
text book makers, but which, in a few particulars, differ somewhat 
from that usually observed in other publications. They divided 
all geologic time into eleven periods and gave the following names 
and limitations: 
“Mhe first [the latest] period shall cover the time beginning 
1 Tenth Annual Report Director U. S. Geological Survey, p. 65, Washington, 1890. 
