344 HALL AND SARDESON PALEOZOIC FORMATIONS OF MINNESOTA. 



very common, particularly in the uppermost layers of the Shakopee. 



This part of the Shakopee carries also that peculiar concretion desig- 

 nated Cryptozoon minnesotense by N. H. WinchelL* Many specimens 

 have been found near Cannon falls, at Northfield, and between Man- 

 kato and Kasota they lie on the prairie in large numbers, weathered out 

 of the rock. These concretions are associated with thickenings of the 

 strata, gentle or strong foldings and a varying vesicular condition. Pro- 

 fessor L. W. Chaney,t who has given some attention to these bodies, 

 reaches the conclusion that their bulkiness is due to a concretionary 

 accumulation. This, with the possibly more ready dissolution and re- 

 moval of the non-concretionary intermediate portions, would account for 

 the existing wavy condition of the strata. 



The shaly condition is occasional in the upper Shakopee, although it 

 is not a marked feature. It occurs in the Saint Lawrence, and is par- 

 ticularly shown in well borings from several towns. Indeed these bor- 

 ings show this member more frequently shaly or arenaceous than other- 

 wise in the southwestern part of the area. 



fr<f^5^fe 





Figure 1. — Fault in the Magnesian near Hastings, Minnesota. 



1 = Jordan sandstone, standing 30 feet above the railway tracks: -j = lower Shakopee dolomite, 

 which to the left of the fault is brought down to the level of the tracks and possibly lower. 

 Sketched from a photograph l>y C W. Hall. 



Faulting among these magnesian beds is ^w\\ in several places. The 

 most notable case is that near Hastings, on the eastern side of the Mis- 

 sissippi, beside the tracks of two railways, the Chicago, Milwaukee and 

 Saint Paul and the Chicago, Burlington and Northern. The extent of 

 slip cannot accurately be determined, but is not less than 50 feet. Fig- 

 ure 1, sketched from a photograph taken by one of the authors, shows 

 the relation of the rocks distinctly seen from the railway trains. With- 

 out discussing the origin of these faults, the opinion may be expressed 



*Geol. and Nat, Hist. Surv. Minn.. 14th Ann. Rep., 1885, p. 313. 

 fBull. Minn. Acad. Nat. Sci., vol. iii, no. 2, 1801, p. 280. 



