LIMITS OF THE LOESS AXD ASSOCIATED DEPOSITS. 537 



From this point the margin seems to have been in the present trough 

 of the Missouri, for all flats north of there are more or less covered with 

 it, while the heights south rarel\^ show it. This relation obtains at least 

 to the east line of Callaway count\\ It has not been clearly recognized 

 on the high swells and knobs in Montgomery and Warren counties. It 

 is certainly not to be found on the knobs in Pike and Lincoln counties. 

 A deposit closely resembling it, if not contemporaneous, covers levels in 

 Saint Charles and Saint Louis counties up to 150 to 200 feet above the 

 Missouri. Its southwestern boundary in Saint Louis county is not far 

 from the Creve Coeur branch of the Missouri Pacific railroad. It does 

 not overtop Grays summit, though very near it. Its limit in this por- 

 tion — that is, in Montgomery. Warren and Pike counties — may be said 

 to correspond approximately with that of the drift, though rising per- 

 haps 25 to 45 feet higher and extending correspondingly farther where 

 the topograph}' j^ermits. 



It should stated, however, that as the margin of the drift declines very 

 much along the Dardenne and Cuivre rivers, so also with the loess or gray 

 clayey loam. The two do not lose their relations to each other, though 

 they cover the hilltops and hillsides like a blanket. 



It should be noted also that the eastward slope, which prevails in Saint 

 Charles county from its western boundary nearly to the great rivers, 

 shows a deep yellowish clay, which differs from the graj'^, loamy clay, 

 though the exact relation of the two I have not very clearly determined. 

 The yellow, I think, is a preglacial residuary clay of Carboniferous origin. 



Terraces, Ancient Channels and Rapids. 



It is found convenient to treat these together. While we have already 

 stated that the Pleistocene area was mainly a plain, we wish noAV to 

 make an important modification of that statement. There are quite 

 extensive areas occupied by high terraces, which are mostly formed by 

 deposition. The principal one rises from 125 to 175 feet above the present 

 Missouri. Others much less conspicuous are found along the Grand 

 river and other tributaries to the Missouri, both north and south. A few 

 small patches of a similar formation occur along the Mississippi at lower 

 altitudes. This principal terrace generally consists of from 30 to 50 feet 

 of buff loess, with two or three thick strata of reddish clay underneath. 

 Below, this clay it is often interstratified with chert, pebbles and northern 

 drift, sometimes intermixed so as to closely resemble till. In other cases, 

 the sand and gravel may form the lower half of the terrace, 25 to 50 feet 

 in thickness. This terrace sometimes shows rock very high in its mass, 

 while in other localities the stratified terrace deposits extend down to the 

 level of the present stream or even below. 



