14 Illinois Natural History Survey Circular 49 



fossil pollen finds indicate that if modern man could have walked 

 through one of those forests he might have thought himself in a 

 forest of today. He would have found pines, witch hazel, oak, and 

 sycamores very much like those of today. But mixed with them would 

 have been a few strange plants. Analyses of various groups of insects 

 indicate that he would have found many familiar insects, includ- 

 ing termites, mosquitoes, caddisflies, bees, flies, beetles, and bugs. 

 Whether these ancient Cretaceous forests were coniferous forests 

 with a scattering of deciduous trees or the reverse we do not know. 

 There is no evidence of anything like the Great Lakes during the 

 Cretaceous Period ; at that time the present Lake Michigan area was 

 probably part of a continuous forest. However, the area was not far 

 from the ocean, which had inundated much of North America, as 

 illustrated in fig. 9. 



SEHING THE MODERN SCENE 



The Cenozoic Era is divided into a relatively long period, called 

 the Tertiary Period, and a short one, called the Quaternary, embrac- 

 ing chiefly the Ice Age and the time since then. Soon after the 

 beginning of the Cenozoic, North America lost most of its continental 

 seas, fig. 9. The general outlines of the continent have changed little 

 since then. In an early, long epoch, the Eocene, the North American 

 climates appear to have been warmer than those of today; in later 

 epochs the climate of the northern and central portions became more 

 temperate. 



By the Oligocene Epoch, possibly 35 million years ago, at least 

 the northern portion of Illinois was probably covered by a temperate 

 deciduous forest that looked almost like that of the present. Fossil 

 evidence indicates that this forest contained species of oak, hickory, 

 linden, beech, sycamore, and many other trees that were remarkably 

 similar to those living today. The temperate deciduous forests of that 

 time differed in one important respect from those of today. They 

 stretched in an unbroken band from the Atlantic coast of North 

 America, across the continent, through Alaska, and across Eurasia 

 to westernmost Europe. Thus, forest trees that may have originated 

 in various areas of the northern land masses had an opportunity to 

 disperse among the continents. The mixture of trees thus formed 

 undoubtedly resulted in a temperate deciduous forest of greater com- 

 plexity than had existed in any one place before. 



At some time after this, chiefly in the Miocene Epoch, probably 

 20 million years ago, the crust of the earth underwent a period of 

 activity that eventually resulted in a number of striking upheavals. 



