EOLIxiN DERIVATION OF .^FAIX LOESS 173 



banding effects which sometimes occur concentric with the surfaces of 

 the underlying rock or till nuclei. 



If, as we have assumed, the oxidation is dependent on the manner of 

 deposition, it would naturally be expected that, providing the accumu- 

 lation took place in the absence of vegetation and with sufficient rapidity, 

 unleached and unoxidized deposits identical, except for the horizontal 

 stratification and topographic expression with the marl-loess, would be 

 found. The necessary conditions, with one exception, appear never to 

 have been completely fulfilled, for at only one point, namely, on the hills 

 2^ miles northwest of Owensville, has eolian silt resembling the marl-loess 

 in its unleached and unoxidized character been found. The silt at this 

 point reaches nearly to the crest of the hill at 540 feet, and is indistin- 

 guishable from the marl-loess in color, texture, and in the amount of 

 lime present. No fossils were found, though there is no reason, unless 

 because of an absence of vegetation, why gasteropods should not have 

 originally been present. No stratification was observed. Between this 

 eolian type of marl-loess and the common loess there are many grada- 

 tions, though most exposures show a closer resemblance to the latter 

 than to the former. 



Conclusions 



In summarizing the paper it may be said that the writers divide the 

 loess of the lower Wabash valley and vicinity into two distinct types — 

 (1) the marl-loess type and (2) the common-loess type. The first is 

 regarded as practically always of aqueous origin, as far as the region in 

 question is concerned, onl}'' one instance of probable eolian loess of this 

 type having been observed. The common loess, while it can not be sub- 

 divided on physical and chemical grounds, has been separated into two 

 portions on the basis of its topographic expression. Those portions 

 occurring in a belt just outside the marl-loess deposits and marked by 

 the flats and silted divides 500-foot level are thought to be probably in 

 the main of aqueous origin, while the great mass of silts forming the 

 general mantle covering southern Indiana and Illinois are considered 

 as being of eolian origin. The conclusions are regarded as being prob- 

 ably applicable to the general loess sheet of southeastern Illinois and 

 southwestern Indiana, but should not be extended to more remote 

 regions. 



The widely varying views held by different geologists, and especially 

 the variation in the character of the evidence cited in the support of their 

 theories, would seem to make it almost beyond question that the argu- 

 ments are not everywhere based on the same class of deposits. The view 



