PETROLEUM POSSIBILITIES OP PLORIDA 
57 
Permian, Pennsylvanian and Ordovician formations. In Oklahoma, oil 
is obtained chiefly from the Pennsylvanian and Mississippian forma¬ 
tion. The Ordovician, Silurian and Pennsylvanian produce oil in the 
Lima Fields of Indiana and Ohio. The Mississippian and Pennsyl¬ 
vanian yield oil in Illinois. In the Appalachian Fields extending through 
New York, Pennsylvania, Ohio, West Virginia, Kentucky and Ten¬ 
nessee, production is obtained from formations of the Devonian, Mis¬ 
sissippian and Pennsylvanian systems. 
SURFACE INDICATIONS 
Oil in the underlying formations is in some instances indicated by oil 
or gas seeps at the surface. It is, however, not to be assumed that seeps 
at the surface in all instances indicate oil in commercial quantities below 
the surface. On the other hand, it is also not to be supposed that oil 
below the surface will necessarily show as seeps. On the contrary, many 
valuable oil pools have been found of which there was, so far as known, 
no surface indication in the form of oil seeps. 
Many reported oil and gas seeps are found on investigation to be 
something other than seeps of oil or gas. An iron oxide scum is very 
frequently mistaken for an oil scum. Iron is one of the very common 
mineral ingredients in soils, and where iron is present in some appre¬ 
ciable amount, the water of springs and small streams is very com¬ 
monly covered with an oil-like scum;. When an iron oxide scum is 
broken or disturbed it does not quickly reunite. An oil scum, on the 
contrary, reunites at once; an oil scum also if rubbed on the hands is 
not easily removed, while the iron oxide scum is readily removed by 
washing the hands. 
Some gases other than petroleum gases are at times found coming 
from the earth. Thus, from some springs such gases as carbon dioxide 
or hydrogen sulphide are occasionally found escaping. Of these gases, 
however, carbon dioxide will not support a flame, and hydrogen sulphide 
may be recognized by its offensive odor. Not infrequently the presence 
of marsh gas is taken as an indication of the presence of petroleum. 
Marsh gas or methane is a gas of the paraffin series of petroleum com¬ 
pounds. This gas is, however, frequently found in decaying muck in 
bogs and swamps, and for that reason its presence does not necessarily 
indicate a gas seep from any considerable depth. In the case of marsh 
