IOWA ACADEMY OP SCIENCES. 
47 
that the various bitumens, including natural gas, are genetically 
connected with and are closely allied to marsh gas, and that 
they are produced by the natural decomposition of organic 
tissue. Natural gas closely resembles in composition the 
inflammable marsh gas which is often observed coming from the 
muddy bottoms of stagnant ponds. The following analysis, 
giving the mean results of seven analyses made for the United 
States Geological survey by Prof. C. C. Haward, will show the 
composition of natural gas: 
Marsh gas 93.30 
Nitrogen 3 28 
Hydrogen 1.76 
Carbon monoxide. .53 
Oxygen 29 
Olefiant gas .28 
Carbon dioxide.... ... .25 
Hydrogen sulphide 18 
Total 100.03 
Marsh gas, the principal constituent, is a simple compound 
of carbon and hydrogen in the proportions of 75 per cent of the 
former to 25 per cent of the latter. 
The natural gas of the Pleistocene deposits of Iowa is then 
simply the product of the decomposition of the vegetable 
remains buried in the drift. 
RESULTS OF RECENT GEOLOGICAL WORK IN 
MADISON COUNTY. 
BY J. L. TILTON. 
OUTLINE. 
1. The geological formations of the county. 
2. The distribution of the alluvium, loess and drift. 
3. The relation of present drainage to preglacial drainage. 
4. Terraces. 
5. The areas occupied by the Des Moines and Missourian stages of 
the coal measures. 
6. The transition from the Des Moines to the Missourian stage. 
It is intended in this paper to state briefly some of tie 
geological features of Madison county as obseived during the 
