Another global observation of similar significance is the vertical stacking of hydrocarbons deposits, Kudryavtsev's Rule: "Any region in which hydrocarbons are found at one level will be seen to have hydrocarbons in large or small quantities, but at all levels down to and into the basement rock." The most common sequence is to find gas at the deepest levels, oil above, sometimes more gas above the oil, and coal at the shallowest. If one examines gas, oil and coal maps of different parts of the globe, one finds this rule repeated very frequently. It holds in most of the Middle East: many oil wells in Iran have penetrated through large coal deposits. Deep underneath the oil of the Gulf States, large gas fields have been discovered. Almost all the oil wells of Java and Sumatra have drilled through coal, and even the deep gas of Oklahoma is often underneath coal. What we are seeing is principally a succession of hydrocarbons with diminishing hydrogen content as one goes from the deepest to the shallowest. One presumes that bacterial action, which attacks the hydrogen rich hydrocarbons first, has been largely responsible for the progressive hydrogen depletion of upwelling hydrocarbons. For coal, the situation is more complex because biology can be involved in another way also. In a hydrocarbon outgassing area, the ground water is held strongly anoxic because hydrocarbon oxidizing bacteria are abundant there, and quickly remove atmospheric oxygen carried in that water. The result is that the normal processes of fermentation of plant material, which would turn the carbon back to the atmospheric CO2, will be interrupted. Hydrocarbon outgassing areas tend to become swamps filled with the insoluble carbon of plant material. What plant fossils there are in bituminous coal (frequently there are none) are often themselves filled with the same homogeneous coal as that which surrounds them, suggesting a carbon source different from the fossilized plant material itself. It would not seem possible that plant material was converted into the homogeneous coal, and yet that a fraction survived as fossils with a precise maintenance of detail; and that this was then filled by the homogeneous coal derived from similar material.
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