147] FLORA OF COLUMBIA AND VICINITY 5 



which ecologically must be considered a pond, since no vegeta- 

 tion of a strictly lacustrine type has yet been developed, is also 

 of artificial origin. While gradually gathering to itself an aqua- 

 tic and amphibious flora, its influence on the vegetation is still 

 slight. The Wabash railroad crosses this region. Farther 

 north — approaching Centralia — the prairies begin, but have not 

 yet been studied. 



2. The Hinkson region east. — The most striking fea- 

 ture here is also artificial, the waterworks dam. North of the 

 dam the cliffs are for the most part low, though south of the 

 dami, and as far as the Ashland road, they become bold and pre- 

 cipitous. They stand on the east side of the stream at the dam 

 and for a short distance southwest of the dam where, however, 

 they are not especially high. The immediate country is broken 

 by valleys and streamlets into hills, but farther back the plain 

 is gently undulating. The dam has developed extensive muddy, 

 occasionally sandy, flats. 



3. The Grindstone region southeast. — Grindstone 

 creek makes a feint of joining the Hinkson just east of where 

 the Ashland road crosses the latter stream. A little tongue of 

 high land scarcely a rod in breadth separates the valleys of 

 the two streams. This slight elevation soon rises into a nar- 

 row, but high and precipitous, wall of rock, which, making a 

 curve concave to the northeast, finally disappears near where 

 Black's Mill road crosses the Hinkson due south of Columbia, 

 and allows the Grindstone to join the Hinkson at that point. 

 The general trend of the valley of the Grindstone is northeast- 

 southwest, fla,nked on either side by steep cliffs or high bluffs 

 and is usually narrow. These and the plain, back of the cliffs 

 are better wooded than any other portion of the area. 



4. The Hinkson region south. — Immediately south 



