368 The American Geologist. June, 1901 
the introduction of life on the globe can furnish neither gas 
nor oil ; and the fact that such rocks ma}' be reached in Iowa at 
no great depth makes it possible to explore the whole of the 
possibly productive series with comparative ease. Owing to 
their low specific gravity, oil and gas are displaced by descend- 
ing waters and tend to rise toward the surface. They may, 
therefore, be found at some distance above the beds in which 
they are generated, but it would be very unusual to find them 
lower down. 
The seas were practically destitute of life when the Algon- 
kian quartzytes at the base of the Iowa geological column were 
laid down, and all rocks older than the quartzytes were formed 
under conditions even less favorable. It may be very positive- 
Iv affirmed that explorations for oil or gas below the top of the 
Algonkian are certain to be fruitless. Above the Algonkian 
lies a body of Cambrian sediments — mostly sandstones — 1,000 
feet in thickness. Life was far from abundant in Iowa during 
the deposition of the Cambrian, though even if it had been 
never so prolific, it would have counted for little, since sand- 
stone is not a good conser\'ator of the organic matter present 
in the seas at the time of its accumulation. Sandstones are 
good reservoirs for the storage of gas and oil after these prod- 
ucts have been generated from some underlying productive 
rock. But there is nothing below our Cambrian from which 
gas or oil could be derived, and so the probability of finding 
either below the top of the Cambrian sandstones is so small as 
to be unworthy of consideration. Overlying the Cambrian are 
two formations, the Oneota and the Saint Peter, equally as bar- 
ren as anything below them. When the drill reaches the top 
of the Saint Peter sandstone, it has practically passed through 
and beyond all formations in which there is any possible hope 
of finding the products under discussion. Next in ascending 
order comes the Trenton limestone, a formation that was laid 
down on a sea bottom fairly crowded w'ith swarming forms of 
life. This limestone is impure ; it contains a large amount of 
clay mixed either with the materials forming the layers of 
stone or laid down as beds of shale between the more stony lay- 
ers. The Trenton formation was deposited under exceedingly 
favorable conditions for making it a productive source of gas 
and oil. It still contains large quantities of bituminous mat- 
