164 FULLER AND rLAlT MARL-LOESS OF LOWER WABASH VALLEY 



situation and texture of this type is more favorable to oxidation, or (3) 

 that it was oxidized at the time of its deposition. Analyses show that 

 the first assumption is untrue, and the field examinations of the occur- 

 rence of both types, together with comparative studies of the textures, 

 show that the second assumption likewise fails to hold good, the condi- 

 tions being in fact more favorable to the oxidation of the marl-loess than 

 of the common type. It is thought, therefore, that the difi'erences in 

 oxidation and leaching date back to the period of deposition, the condi- 

 tions favoring oxidation being pronounced in the case of the common 

 loess and of little importance in the case of the marl-loess. A rapid 

 accumulation in the absence of vegetation, and especially in the pres- 

 ence of water, would afford the simplest explanation of the observed 

 lack of oxidation. 



The greater coarseness of the marl-loess may be taken as indicating a 

 more powerful transporting agent than is indicated by the finer material 

 of the common loess. This is especially true of the pebbles which occur 

 up to half an inch or more in diameter, and in positions which preclude 

 a derivation from any nearb}^ drift deposit. Some of the largest and 

 most abundant pebbles were found over the top of a marl-loess flat, at 

 a distance of half a mile or more from the nearest available source, from 

 which the flat on which they were found is separated by a valley which, 

 in part at least, appears to have been determined by an original depres- 

 sion. In the instance in question it seems certain that no agent other 

 than water could have accomplished the observed transportation and 

 distribution of the pebbles. The high calcareous constituent of the 

 marl-loess, as compared with the common loess, indicates, as in the 

 case of oxidation, an accumulation of the former under conditions rela- 

 tively much less favorable to weathering. An accumulation under water 

 or a very rapid accumulation on the land is thought to afford the best 

 explanation of the observed differences. 



The perfection of the stratification, consisting, as it frequently does, 

 of very regular and perfect, though minute, horizontal laminations, is 

 in marked contrast with both the steeply dipping layers characteristic 

 of the accumulations at the front of advancing dunes (lower right-hand 

 portion of figure 2, plate 14), or of the wavy banding characterizing 

 wind-blown materials which have accumulated on dunes covered partly 

 or wholly with vegetation (upper portion of exposure, figure 2, plate 

 14). It is of a character which in any other substance than a supposed 

 loess would unhesitatingly be referred to an aqueous origin. Its peb- 

 bles, as has been noted, occur frequently in situations and of a size 

 which would appear to bar out wind action as an agent in their accu- 

 mulation. The occurrence of the stratification in repeated instances up 



