145] FLORA OF COLUMBIA AND VICINITY J 



between two geological formations, that of the coal measures 

 to the north, and that of the lower carboniferous limestone to 

 the south. The flora of the coal measures is properly prairie, 

 while that of the limestone is the deciduous forest of the Ozark 

 plateau. The flora is then one of tension between forest and 

 prairie. The prairie vegetation is that of Illinois and Iowa; the 

 forest vegetation is that of the Ozark plateau of Missouri and 

 northern Arkansas, which is much like that of Indiana, Ohio 

 and southern Michigan except that the beech and pine are ab- 

 sent. 



Besides these two great floras there are three others, which 

 are subordinate. The bottoms of the Missouri bring hither the 

 alluvial flora of the great rivers of the central plain. In the 

 ponds and marshes occurs the hydrophytic flora of the eastern 

 United States, many species of which cross the continent. On 

 the cliffs and ledges is the limestone rupestrine flora. Other 

 elements may be described as accidental. The floods of the Mis- 

 souri bring waifs from the great plains, others come along the 

 railroads; while man has brought with him the weeds and cul- 

 tivated plants from over the sea. 



3, THE PHYSIOGRAPHY OF THE REGION. 



The geology of the region about Columbia is simple. All 

 to the south, southwest, west and northwest belongs to the lower 

 carboniferous limestone, all to the north and east to the coal 

 measures covered with glacial clay. The rocks dip to the north. 

 Where the clay has been eroded, as in the valleys and along 

 the streams, the limestone ledges appear. Southward near the 

 Missouri the loess formation occurs, where the Missouri ap- 

 pears to have been the southern boundary of the glacial ice 

 sheet. Geologically the area is divided into a northern and a 

 southern realm. While in the vegetation there is no sharp di- 



