154 MISSOURI BOTANICAL GARDEN, 



^i V ^J;^ till liitunjGLiii^ tiuuuuj 



sinkholes, which is quoted 

 ^^Mr. Say descended in1 

 ascertaining the medium 

 the earth. This sink ODei 



to 



under these 



below 



■h 



deep 



is admitted, and each large enough to afford passage to the 

 body of a man. Within are two chambers from G to 12 feet 

 in breadth and 35 feet long. At the bottom of the second 

 chamber is a pool of water rather difficult of access. In this 

 apartment the mercury stood at 60"^ F., in a sliady part of the 



about 



The 



t> 



75° F." 



demonstrated 



in the city of St. Louis are used as wine-cellars, as for in- 



under 



and 



of 45° F., varying but little if at all. Similarly 



Company 



or Indian Cave, 13 miles 

 led as a cellar by the Cliff 



The principal modification of the upland is the ravine, 

 resulting from erosion by i^erennial streams. It is an open 

 question whether several of these ravines were not formed, 

 in part at least, by solution of the limestone by underground 

 streams, followed by a subsidence of the earth's crust. That 

 this happens rather frequently is shown by Nason* and it is 



very 



for 



exactly this manner, followed by erosion by surface streams. 



The Missouri plateau, at least south of St. Louis as far as the 



mouth of the Meramcc River, ends abruptly, the limestone 



cliffs overhanging the river, the stratification of the St. Louis 



bei 



but 



hold especially since the erosion by the river in earlier days 

 left numerous concave surfaces. At the base of these bluffs 

 is a small amount of talus, together with colluvial soil brought 



* Nason, F. L. A Report on the Iron Ores of Missouri. Missouri Geo- 

 logical Survey. 2 : 90. 1892. 



