
GEOLOGICAL MAPS AND SECTIONS 329 
on some imaginary line drawn at any distance below the 
surface. 
Vertical Sectzons—These are sections so drawn as to 
_show all the strata piled up, as it were, in a tall column in 
their proper order of succession. Where no unconformities 
occur, the dip of the strata is usually neglected, and the beds 
are arranged in a horizontal position. As sections of this 
kind are meant to show in detail the succession of the strata 
in a coal-field or other area containing beds and seams of 
economic importance, they are drawn on a large scale—a 
much larger scale than would be employed in the construction 
of even the most elaborate profile section. In the case of 
vertical sections great accuracy is required—the thickness of 
each individual bed being carefully measured in exposed 
rock-sections, or obtained from other reliable sources, as from 
records of the rocks passed through in sinking wells, pits, 
bore-holes, etc. The Geological Survey publishes sheets of 
such sections to show the succession of beds encountered in 
our coal-fields. By comparing the vertical sections illustrating 
any particular coal-field, we can see at a glance how the same 
series of strata varies as it passes from one part of the coal- 
field to another. Similar vertical sections, usually on a much 
smaller scale, are now and again constructed by geologists 
for the purpose of comparing the succession of strata met 
with in one place with that encountered in some other area 
where rocks of the same age occur. It is, in short, a graphic 
method of showing how the same formations and systems 
vary in character as they pass from one region to another. 
