PREFACE 



During parts of the field seasons of 1905, 1906, and 1907, the Illinois 

 Geological Survey had the valued services of America's dean of Carbonifer- 

 ous paleobotany, Dr. David White, in a general reconnaissance of the 

 Upper Coal Measures, now precisely referred to as the Pennsylvania!! 

 system. Previous to that time but little work had been done, chiefly by 

 Leo Lesquereux from collections by A. H. Worthen and associates. White's 

 work led to a general correlation of the strata of the Illinois coal field with 

 the eastern field, and to a division of the Pennsylvanian system into three 

 series: the Pottsville (lowest), the Carbondale, and the McLeansboro. 



In 1921, in connection with an intensive study of the coal resources 

 of Illinois, the State Geological Survey undertook a program of a more 

 detailed study of the plant forms found in strata associated with the coal 

 beds, fully realizing that the facts to be uncovered by such an investiga- 

 tion w r ould likely be of inestimable value to a proper correlation of the coal 

 beds in different parts of our State and to our knowledge of their extent 

 and relationships. The work is being conducted by Dr. A. C. Noe, Asso- 

 ciate Professor of Paleobotany of the University of Chicago, and has already 

 reached an advanced stage. 



The study is far-reaching in its relations to the functions of the Geolog- 

 ical Survey, to the proper identification of coal beds which the Survey 

 uses in determining the existence of favorable structures for the com- 

 mercial occurrence of oil and gas, to the estimates made of the State's 

 coal resources, to the scientific contributions which the Survey is in posi- 

 tion to make on both the character of the vegetation, climatic environ- 

 ment, and physiographic conditions of the Pennsylvanian period, and on 

 the life history of the plant kingdom, and finally, with unneglected atten- 

 tion, to providing secondary schools and colleges of the State with desir- 

 able educational material. 



It is designed eventually to publish a comprehensive monograph on 

 the flora of the Pennsylvanian system of Illinois, properly illustrated and 

 containing descriptions of both old and new species, and the conclusions 

 to be drawn regarding coal correlations. The field, however, is very exten- 

 sive, and, in order that advantage may be taken of data obtained in the 

 course of the study, short bulletins covering sub-units of the State will be 

 issued. The present bulletin is an account of the Pennsylvanian flora of 

 northern Illinois, marking the completion of the work of one of the sub- 

 units. Its treatment is feasibly popular, and such technical descriptions 

 as new and old species may require are left for the monograph. 



M. M. Leighton, Chief, 



State Geological Survey. 



