The young man on this month's 

 cover, Johnny Kolias, U, of El- 

 wood, Indiana, is obviously im- 

 pressed by Field Museum's skele- 

 ton of a Pleistocene mammoth, 

 Mammuthus primigenius. The 

 mammath occurred over much of 

 North America and as late as 

 ten thousand years ago, could still 

 be found in the Great Lakes Area. 

 Both mammoths and mastodons, 

 a related elephant-like species, are 

 featured in Field Museum's Ses- 

 quicentennial Tour of Illinois nat- 

 ural history. 



The corn snake (Elaphe guttata) 

 at right is common near farms 

 throughout Illinois. It is a harm- 

 less, useful snake, feeding on mice. 

 The corn snake, which has a dis- 

 tinctive pale red-orange body with 

 deep red markings, is one of near- 

 ly fifly snake species in Illinois. 



Sesquicentennial Special 



HALF A BILLION YEARS 

 OF ILLINOIS HISTORY 



Despite remarkable advances and changes in the life 

 patterns of Illinoisans in the past 150 years, the history 

 of our statehood is as brief as the flick of an eyelash in the 

 hundreds of millions of years of Illinois' natural history. 

 In observance of this Sesquicentennial year, Field Museum 

 has arranged a special self-conducted tour to acquaint res- 

 idents and visitors with the state's varied and complex past. 



Areas of geology, zoology, botany and anthropology are 

 deeply interrelated in the history of Illinois, of course, but 

 its story begins with the forces which shaped the earth. 

 The area which would become Illinois was subjected to a 

 variety of geologic and climatic changes but its position 

 during two particular geological periods were of great im- 

 portance in giving the state its significant agricultural and 

 economic value in modern times. 



The bedrock of the Chicago area and the extreme north 

 central part of the state is largely of the Silurian Period 

 (about 420 million years ago) but almost the entire re- 

 maining land area in Illinois dates to the Pennsylvanian 

 Period (about 250 million years ago), the one geological 

 period during which climate and plant life in combination 

 permitted the formation of coal beds. 



Illinois was part of the continent that was partially 



covered by vast inland seas which retreated and advanced 

 over several geologic periods. The most recent period on 

 record of an inland sea in Illinois is in the Cretaceous 

 Time (about 100 million years ago), although it is possible 

 that parts of Illinois may have been undersea even later. 

 A legacy of marine fossils testifies to the aquatic nature 

 of life forms in Paleozoic Illinois. 



Between the advance and retreat of the Pennsylvanian 

 sea, the Illinois landscape was frequently swampland, in- 

 cluding extensive forests which died, decayed and were 

 buried under the sediments. Millions of years later these 

 dead forests became the rich coal deposits that were of 

 such economic importance in the 19th and 20th centuries. 



The life in those ancient giant fern-tree forests included 

 unusual and now extinct fishes, insects and invertebrates 

 as well as many archaic plants. Amphibians were already 

 diverse and the reptiles, later to dominate the animal world 

 because of their great size and variety, were beginning 

 their evolutionary ascent. Illinois has one of the world's 

 three most significant fossil records of life in its Mazon 

 Creek formation. Because soft parts of fossil animals and 

 plants are preserved in concretions, scientists are able to 

 do detailed studies of aspects of ancient life usually un- 



Pnge2 JULY 



