HOUSTON COUNTY. 227 



Drift.] 



from a pencil sketch, is one of the results of wind erosion, seen in the valley 

 of Thompson's creek, near Hokah, situated near the top of the St. Croix 

 sandstone. 



THE DRIFT. 



The true northern drift is not spread over this county. It contains no 

 drift clay, nor boulders of foreign origin. There is a thin deposit of foreign 

 gravel at Riceford, in the extreme southwestern part of the county, and 

 there is a terrace along the Mississippi river that is made up of gravel and 

 sand of northern origin, but the county wholly escaped the operation of 

 those forces which spread the well-known drift clay and boulders over the 

 most of the state. Whether any former glacial era caused it to be covered 

 with the ice of a northern glacier cannot be determined, since the mate- 

 rials left by that era, if any there were, may have been decomposed, and 

 may have entered into the stratified clays and the soils of the Mississippi 

 valley further south, under the combined influence of time and the destruc- 

 tive forces of later eras. 



There is to be seen occasionally a local drift, or debris derived from 

 the rock of the country round about, and this sometimes has a deceitful 

 resemblance to true northern drift, yet it can always be distinguished from 

 it on examination. On the northwest quarter of section 25, Caledonia, along 

 the road, near the brow of the Shakopee limestone, there is a bank of such 

 loose materials. There is a cut of about three feet, which consists mainly 

 of rusty loam, rather sandy, embracing large masses of black quartzyte, 

 which also vary to a lighter color but show very little, if any, lime. Other 

 lumps consist of pyrite crystals, now converted to limonite, and of rusty, 

 hardened sandstone, perhaps from the Jordan. These last indeed comprise 

 perhaps a majority of the stony masses. There are also large quantities 

 of ordinary chert and an occasional piece of water-worn limestone. The' 

 bank shows no stratification, but consists of these materials simply mingled 

 with the loam. The whole appears red and rusty, but discloses not a single 

 piece that cannot be referred to the Cambrian rocks.* 



Alluvial terraces. There is a marked alluvial terrace that accompanies 

 the Mississippi and Root rivers, and ascends their lower tributaries, but it 



*As to the cause of the "driftlessarea", compare the fifth annual report, p. 35. 



