282 THE GEOLOGY OF MINNESOTA. 



(St. Lawrence limestone. 

 t 



sandstone and tains, which is supposed to consist mainly of sandstone, rise 

 375 feet above the river. Near the upper portion of the sandstone a con- 

 spicuous terrace or line of frequent exposure, producing a shoulder, may be 

 seen along the creek in entering Rushford from the south. 



The St. Lawrence limestone. This is the lowest portion of the Lower 

 Magnesian formation of Dr. D. D. Owen. In the annual report for 1873 the 

 geology of the Minnesota valley is given. It is there announced that the 

 great formation to which the name Lower Magnesian had been applied, con- 

 sists of three distinct members two limestones separated by a sandstone 

 and the names of the localities where these members have their character- 

 istic outcrops, in that valley, were applied to distinguish them, as they 

 were certain to play an important part in working out the detailed geology 

 of the eastern portion of the state. 



The area of this limestone is embraced in one with that which on the 

 accompanying plate includes also the areas of the Jordan and Shakopee 

 formations. Along the river bluffs nearly to Rushford it is found only in 

 the lower portion of the limestone belt, as the Jordan sandstone and Shak- 

 opee limestone are both preserved and overlie it, but toward Rushford this 

 limestone begins to be the only one that is found in the bluffs, the upper 

 members of the Cambrian having a strike across the country some miles in 

 either direction away from the immediate valley, There are places, how- 

 ever, even further east still, where the overlying Jordan and Shakopee are 

 preserved and appear in the tops of the river bluffs. The St. Lawrence ex- 

 tends in the bluffs of the Root river to some distance above Isinour's station, 

 and nearly to the lower mill at Preston. The valley of Watson's creek at 

 Isinour's station is cut about twenty-five feet into the St. Lawrence. At 



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Lanesboro the amount of the St. Lawrence visible is about 195 feet. At 

 Whalen 155 feet are seen in the upper portion of Whalen's bluff. At 

 Rushford the uppermost 190 feet of the bluffs are of the St. Lawrence. The 

 thickness of the formation is not far from two hundred feet. 



The St. Lawrence in Fillmore county is a dolomitic limestone, with some 

 of its layers distinctly arenaceous, and stained with green sand. In general 

 its bedding is regular and evident, but there is a thickness of about fifteen 

 feet near the bottom of the formation in which the bedding is confused, or 

 the layers are lost horizontally Below this confused bedding are, however, 



