LETTER OF TRANSMITTAL 



State Geological Survey Division, March 5, 1929 



Hon. A. M. S ltd ton. Chair man, and Members of the Board of Natural Re- 

 sources and Conservation. 



Gentlemen: — I take pleasure in transmitting herewith, for publication 

 Is Report of Investigations No. 18, the manuscript of the paper entitled 

 "The Gastropod Genus Yvania: Contribution to the Paleontology of Illinois," 

 by Dr. J. Marvin YYeller, Paleontologist on our Geological Survey Staff. 



This is the first of a series of pa]>ers which will give the results of our 

 paleontological studies of fossil forms belonging to the Pennsylvanian (Coal 

 Measures) system of Illinois. As you are aware, these studies are for the 

 purpose of determining the composition, evolution and history of the Penn- 

 sylvanian faunas and of ascertaining what fossil forms may be used as horizon 

 markers in correlating isolated outcrops of Coal Measures strata; this in turn 

 is fundamental in determining the coal resources of the State and in working 

 out geologic structures to be tested for commercially valuable accumulations 

 of oil and gas. The genus dealt with in tins particular paper belongs to the 

 most characteristic family of gastropods represented in our Coal Measures 

 strata. 



Very sincerely yours, 



Morris M. Leigiitox, Chief. 



