106 



SCIENCE 



[N. S. Vol. XLI. No. 1046 



is water deposited or has any stratification ex- 

 cept in certain places where it has a very ob- 

 scure banding roughly parallel to the present 

 surface such as loess commonly displays. 



However, some of the material included 

 under the head of " marl-loess " has a very 

 distinct and approximately horizontal strati- 

 fication. Most such material is sand of fairly 

 uniform grain, but layers and lenses of grav- 

 elly sand, calcareous sand, and also clay and 

 silt are common. The lime is especially abun- 

 dant in the lower ends of tributary valleys. 

 But, so far as the writer could find, this 

 material is not present at a greater altitude 

 than 440 feet or about fifty feet above the flood 

 plain, and it appears to him to be a part of a 

 widely developed system of valley fillings, rem- 

 nants of which he has traced through nine 

 states in the upper Mississippi Basin. The 

 tops of the remnants are generally 40-60 feet 

 above the present flood plains. The valley 

 fillings seem to have grown as units notwith- 

 standing the fact that some streams are greatly 

 overloaded and others not at all. It thus 

 happened that some tributaries were ponded oy 

 the filling in the main valleys into which they 

 discharged, and the deposits laid down in such 

 comparatively quiet water are fine-grained and 

 calcareous, the lime being largely in the form 

 of small irregular masses differing somewhat 

 from loess kindchen and possibly secreted by 

 plants. 



Whatever the origin of the stratified mate- 

 rial, surely it is not correct to call it loess, for 

 it differs markedly in several respects from the 

 material known by that name elsewhere, par- 

 ticularly at the type locality in Germany. 

 The principal respects are that it is hetero- 

 geneous, being made up of material of all 

 degrees of fineness from clay to gravel, whereas 

 loess is very homogeneous; (2) that it is co- 

 extensive with the valley fillings above referred 

 to. Thus the " good sections of a very siliceous 

 form of the marl-loess ... in the bluffs at 

 Mt. Carmel," the writer would call good ex- 

 posures of waterlaid terrace sand, having no 

 relation whatever to the true loess. 



It seems, further, that some wind-blown sand 

 has been included in the " marl-loess." The 



vaUey filling along the Wabash has been the 

 source of much dune sand. Most of the dunes 

 are near the valley bottom, but some of the 

 sand has been carried up on the valley side 

 and some even to the top of the bluff and 

 neighboring divides. This seems to have hap- 

 pened in at least two different epochs, and 

 there appear to have been two or more epochs 

 of loess accumulation, though one is most im- 

 portant. As a result the sand and loess finger 

 into each other in places, but in no section are 

 there more than 2 or 3 layers of each. 



It therefore seems to the writer that the 

 " marl-loess " includes 



1. Ordinary bluff loess (the principal part). 



2. Glacial outwash. 



3. Deposits laid down in ponded tributaries. 



4. Wind-blown sand. 



The stratified and sandy material of classes 2, 

 3 and 4 are markedly different from true loess. 



The division of the loess of the Patoka quad- 

 rangle into marl-loess and common-loess ap- 

 pears to have a relation to the fact that on the 

 bluffs near very large streams loess is generally 

 coarser (or at least more free from extremely 

 fine particles) and thicker and more calcareous 

 than at a distance of several miles. The 

 greater part of the material mapped as marl- 

 loess seems to be loess of the ordinary bluff 

 phase. That is to say, it is buff colored, soft, 

 massive, unstratified, homogeneous, calcare- 

 ous, earth. The particles are mostly angular 

 quartz grains, too small to be classed as sand 

 but some of them are clay. It commonly con- 

 tains shells of air breathing animals and is 

 characterized further by a tendency to develop 

 and retain vertical cliffs. 



The fact that both the bluff-loess and the 

 clay-loess are best developed on the east side of 

 the valley seems more reasonably accounted for 

 by the prevailing westerly winds than by pos- 

 tulating that " the main current hugged the 

 western shore," especially since throughout 

 the Mississippi Basin the loess is more exten- 

 sive on the east side of the few main streams 

 than on the west. 



The writer confesses- an inability to see the 

 " terrace form of the marl-loess " as described, 

 the top being said to have a position 500 feet 



