:jS(j THE GEOLOGY OF MINNESOTA. 



[Modified drift. 



In a gravel bank at Albert Lea, according to Mr. Wm. Morin, the jaw 

 bone of a mastodon was found a number of years ago. It was sent to St. 

 Paul, but was lost in the capitol fire in 1881. 



From Albert Lea to a distance of four miles northward, the valley of 

 the Shell Rock river is occupied by modified drift, consisting of stratified 

 fine gravel, sand and silt, or clayey sand. This deposit has an area from 

 one and a half to two miles wide, about two-thirds of its width being on 

 the west side of the stream. Originally this nearly fiat plain was contin- 

 ous from the east to the west side of the valley, through which the Shell 

 Rock river has since cut its channel about forty feet in depth. A portion 

 fully a mile wide remaining on the west side of the river in sections 29, 31 

 and 82, Bancroft, is known as " Itasca prairie",* a little collection of houses 

 in the southeast quarter of section 31 being called " Itasca". The level site 

 of the town of Albert Lea, consisting of stratified fine gravel and sand, is 

 part of the same formation, which here is underlain by a mud or fine sand 

 of dark color, sometimes yielding branches or twigs of wood. Besides the 

 extension of this deposit upon both sides of the Shell Rock river and Foun- 

 tain lake to the west end of lake Albert Lea, it also reaches from Itasca 

 prairie two miles southwestward, by White lake to Pickerel lake, its width 

 for this distance being from one to two miles. It is here nearly level, with 

 its surface about forty feet above Pickerel and White lakes; against which, 

 as also at the end of lake Albert Lea, it is terminated by steeply sloping 

 escarpments. The origin of these beds of stratified drift is believed to have 

 been from the floods formed by glacial melting, chiefly during the final 

 recession and departure of the ice-sheet. It has evidently been in some 

 places excavated by streams since the ice age. Yet it can scarcely be sup- 

 posed that the hollows of all these lakes have been formed by such erosion; 

 in some instances they must apparently be attributed to the presence of 

 masses of ice remaining where the lakes now are, causing their basins to 

 be left empty when the adjacent plains of modified drift were deposited. 



Another remarkable area of modified drift known by the name of " Bear 

 lake prairie," is found in Mansfield and the west end of Nunda, reaching 

 six miles from north to south and the same distance from east to west in 

 this county, while its southern portion continues two miles or more into 



*This was named Paradise prairie by Lieut. Albert Lea. See page 67. 



