280 Cryptozoon Minnesotense at Northfield — Chaney. 



The iron ore found in the gabbro is unquestionably of igneous 

 origin. It is a dull, massive magnetite with feebler magnetic at- 

 traction than the shiny granular ore of the Huronian quartzites. 

 It also differs from the latter in containing titanic acid, ranging 

 from 1 to 30 per cent. Although it is found in mountains which 

 would be almost inexhaustible were they mined, the titanic acid 

 renders the ore undesirable with the present methods of iron smelt- 

 ing. Where beds of the ferruginous Huronian quartzites are 

 found involved in the gabbro overflow, as mentioned above, we 

 seem to have non-titaniferous magnetite from the gabbro itself, 

 but the appearance of the ore generally shows its true nature; and 

 it may be stated as a general truth that the gabbro magnetite is 

 titaniferous. 



Ascending now through geologic time past all the rocks of 

 the Silurian, Devonian and Carboniferous, we find our last iron 

 ore formation to be the Cretaceous. At the bottom of this forma- 

 tion are found beds several feet thick of a low grade limonite ore. 

 It occurs in Fillmore county, where the Cretaceous lies upon the 

 Lower Magnesian, and is reported to be more than thirty feet thick 

 in places. Some of this ore has been used at the furnace at Black 

 River Falls, Wisconsin. It is probably of as good quality and as 

 extensive in quantity as much of the ore formerly mined and 

 smelted in Pennsylvania. But as long as we have mines in the 

 northern part of our state of the best ore in the world, the poorer 

 Cretaceous ore of the southern part of the state will not be used. 



October 8, 1889. 



[Paper GG.^ 



CRYPTOZOON" MINI^ESOTENSE IN THE SHAKOPEE LIMESTONE AT N"ORTH- 



FiELD, MINNESOTA. — L. W. Chaney^ Jr. 



Several years ago I noticed frequently what appeared to be 

 curved strata in the Shakopee limestone at a point near Northfield. 

 A carriage road passed along under the ledges near the river so 

 that one traveling that way could scarcely fail to notice the pecul- 

 iar arrangement. After puzzling somewhat over them, attention 

 was called elsewhere and a railroad having usurped the place of 

 the former carriage road, they were seen but little and forgotten. 



Two years ago Mr. F. 0. Higbee and Mr. W. S. Wingate of 

 the junior class in Carleton College were prospecting for fossils 



