364 E GEOLOGY OF MINNESOTA. 



[Peat. Modified drift. 



spread wider, and flowed at higher levels. But in Mower county the peaty 

 deposit is not confined to the valleys of streams, nor to the proximity of 

 streams. Mower county is on one of the highest divides in the state of 

 Minnesota, and from it flow the sources of streams toward the north, south 

 and east. Those streams are small and never could have flooded the extent of 

 country in which this peat is found. From all accounts it appears to be em- 

 braced between glacial deposits of gravelly clay, and it seems to mark a 

 period of interglacial conditions when coniferous trees and peat mosses 

 spread over the country. Peat mosses are not necessarily restricted to low, 

 wet places. If the atmosphere be moist they will flourish on any surface, 

 and an accumulation of good peat may take place on a bare, rocky moun- 

 tain side. There are extensive marshes now existing in northern Minne- 

 sota, mainly covered with ericaceous plants, with some cedars and tama- 

 racks, that are forming immense peat deposits. With an increase in the 

 amount of moisture of the air such peaty accumulations would spread over 

 much higher levels. A return of glacial conditions would bury such 

 marshes below the deposits that are known as drift. 



But little modified drift has been seen in Mower county. This, per- 

 haps, is partly due to the fact that but little opportunity is afforded in the 

 form of natural or artificial excavations for inspecting its actual composi- 

 tion. The plate of the county is wholly colored as if only the till charac- 

 ters of the drift exist, but a few exceptions should be mentioned. There is 

 considerable gravel in the valley of the Upper Iowa river in Le Eoy town- 

 ship, and in that of the Cedar in Austin and Lyle. From the south bound- 

 ary of the county in sec. 33, Lyle, a flat tract consisting of gravel and sand 

 accompanies the Cedar river northward, sometimes being about two miles 

 wide. This plain rises from twelve to eighteen feet above the Cedar river 

 along the north part of Lyle, and to Austin city. In the north part ot Lyle' 

 a distinct terrace is seen running along the Cedar, one-half or three-fourths 

 of a mile distant, limiting this belt of gravel and sand, and rising gradu- 

 ally about twenty feet above the gravel flat. This terrace gradually ap- 

 proaches the river toward the south, but is cut and disturbed by the en- 

 trance of Woodbury creek. The real cause of it is shown by the strike of 

 the Devonian limestones where they appear in the banks of Cedar river, 

 near the mouth of Woodbury creek, belowwhich the general elevation of 



