ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 



137 



lished by Ladd.* It is understood 



by members of the U. S. Geological Survey 



column should bo modified to some 



As it stands 



accom 



this section along geological lines since its inception by 

 Shumard in 1854 and up to 1890. It was especially the 

 boring of a well at the Insane Asylum at St. LouiSj sunk to 

 a depth of nearly 4,000 feet, which threw light upon the 

 rocks which in no place in this vicinity reach the surf ace. f 



Quaternary Deposits. 



The most detailed descript 



forma 



tion of the Missouri portion of our section is that by Todd. J 



1. Recent Alluvium.— The alluvium deposited by the 

 Mississippi is in part derived from the Missouri River which 

 enters the former about ten miles north of St. Louis. It is 



y composed of sand, with coarser material towards 



mam 



numerous 



the bottom. On top of the sand we find cIj 

 of sand and clay. These deposits, which are 

 variable, both in size and locality, are also the first stages of 

 the sandbar formations. On the west bank of the Mississippi 

 occur wider or narrower bottoms, overflowed at times of flood 



Their subsoil, to a depth of several feet, is a heavy 

 loam laid down by the river. Owing to the growth of tall 



only. 



ti 



summer 



loam 



vegetation forming a rich, black soil. As a result of the na- 

 ture of the shore south of St. Louis, terrace formations are 



absent. 



2. Loess.— This name is applied to the loamy clay which 

 in layers of varying thickness, sometimes as much as 50 feet, 

 overlies the St. Louis limestone, owing its name to its re- 

 semblance to certain sedimentary deposits, thus designated, 



Ladd, G. E. The Clay, Stone, Lime and Sand Industries of St. 

 Louis City and County. Geological Survey of Missouri. Bull. 3. 1890. 



t Broadhead, G. C. On tlie Well at the Insane Asylum, St. Louis 

 County. Trans. Acad. Sci. St. Louis. 3 : 216. 1S7S. 



X Todd, J. E. Formation of the Quaternary Deposits. Missouri 

 Geological Survey. Charles R. Keyes, State Geologist. 10:111. 1S96. 



