352 HALL AND SARDESON EOLIAN DEPOSITS OF MINNESOTA 



The horizontal distril)ution of tliis bed of loess can not so easily be 

 measured. With many interruptions, it probably extends over a con- 

 siderable ])ortion of the Saint Paul lake area outlined by Upham.* 



Another locality in Saint Paul is near the new state capitol now under 

 construction. On the top of a })ure gravel bed or accumulation of modi- 

 fied drift 30 or more feet thick lies a bed of loess 3 feet and more in thick- 

 ness. It is characterized by its clayey consistency, and this is easily dis- 

 tinguished from the dune sand deposits, which are much more frequent. 



ORIGIN OF THE LOESS 



The problem of the origin of the material of the loess of eastern Minne- 

 sota is not further attacked. Its blanket-like distribution, its evanescent 

 relations to the soil above and the uudoul)ted water or ice deposit below 

 strongly suggest that the material springs from the finely subdivided 

 glacial debris which was comminuted and scattered during the j)eriods of 

 the successive ice invasions. 



Touching the further question of evidence that the loess is of eolian 

 rather than aqueous origin, the following [)oints only can be summarily 

 stated : 1. The loess does not occur in any of the thousands of Minnesota 

 lakes, existing and extinct, whose deposits have been dissected. 2. It 

 does occur on the higher levels of the glacial drift. 3. When in relation 

 with the dune sands it is found higher than they, whereas as a water 

 deposit it should be lower — that is, fsxrther from the shoreline of deposi- 

 tion. 4. It is frequentl}^ liable to carr}^ loam within it, thus pointing to 

 zones of vegetation. | 



Dune Sand 



explana rion of its conspicuo usness 



The dune sand is a much more conspicuous accumulation than is the 

 loess. The nature of the material explains this fact. It is due not onh' 

 to its coarseness and otlier physically resistant qualities as a rock, but 

 also to its greater ca})acity to resist the corroding and dissolving proper- 

 ties constituent in and derived from soils. From the scores of localities 

 where it can easily be seen tlie following are cited : 



SNAKE RIVER VALLEY 



Plae City. — An interesting exposure of dune sand occurs at Pine City, 

 Pine county, Minnesota;}: (see plate 34). At this point Cross lake forms 



* Warren Upham : Modified drift in Saint Paul, Minnesota. Bull. Geol. Soe. Am., vol. 8, pp. 183-196. 



t Compare F. W. Sardeson : What is the loess? Amer. Jour. Sci., 1899, vol. vii, pp. 58-GO. 



X This is aiso a spot of historic interest. Tn one of the severe battles fought in the early years 

 of the century between tlie Chippewa and Siou.x Indians the former took advantage of the ele- 

 vated situation and soft fine sand of this dune sand plain to build entrenchments, in which tliey 

 defended tliemselves successfully against their enemies. The profile of the entrencliments is 

 indicated in the picture. 



