FREEBORN COUNTY. 383 



Geological structure.] 



the topography. Again the unusual frequency of any kind of rock in the 

 drift at a certain place, especially if it be one not capable of bearing long 

 transportation, is pretty good evidence of the proximity of the parent rock 

 to that locality. 



Applying these principles to Freebovn county, we find throughout the 

 county a great many boulders of a hard, white, compact, magnesian lime- 

 stone, many others of which have been burned for quicklime. These 

 attracted the attention of the early settlers, and before the construction of 

 the Southern Minnesota railroad supplied all the lime in the county. 

 Although these boulders are capable of being transported a great distance, 

 their great abundance points to the existence of the source of supply in 

 the underlying bed-rock. In the drift also are frequently found pieces of 

 lignite, or Cretaceous coal, which cannot be far transported by glacier 

 agencies. This also indicates the existence of the Cretaceous lignites in 

 Freeborn county. In regard to changes in the contour of the natural sur- 

 face, we see an evenly flat and prairie surface in the western tier of towns, 

 and in the southeastern part of the county, and a hilly and gravelly tract 

 of irregular shape in the central portion. There are two ridges or divides, 

 formed superficially of drift, that occur in the central part of the county, 

 one north of Albert Lea, and the other south of it, separated about eleven 

 miles, as shown by a series of elevations for a preliminary railroad survey 

 by Wm. Morin, already mentioned. What may be their direction at points 

 farther removed from Albert Lea it is not possible to state with certainty, 

 but on one side they seem to trend toward the northwest. Indeed there 

 seems to be a northwest and southeast trend to some of the surface features. 

 Such rough surfaces, and especially the ridges of drift are more stony and 

 gravelly than the flat portions of the county. They mark the location of 

 great inequalities in the upper surface of the underlying rock, the exact 

 nature of which cannot be known. 



In addition to these general indications of the character of the rock of the county, the shaft 

 sunk for coal at Freeborn reveals the presence of the Cretaceous in that poition of the county, and 

 examinations of the nearest exposures in the neighboring county of Iowa disclose the Hamil- 

 ton limestone of the Devonian age. This limestone is exactly like that found so abundantly 

 in the form of boulders in Freeborn county. As the general direction of the drift forces was 

 toward the south, and as the strike of the Hamilton in Iowa is toward the northwest, there is 

 abundant reason for concluding that that formation also extends under Freeborn county. The 

 great distance toward the northwest through which these limestone boulders can be traced with 



