310 THE GEOLOGY OF MINNESOTA. 



[Cretaceous strata. 



remarkably homogeneous, like the white sand deposits mentioned, can only 

 be referred to the immediate proximity of the lower Cretaceous. It could 

 not have been far transported without being mixed with other rock ma- 

 terial. It distinctly points to the existence of a coarse gravel or conglom- 

 erate in the lower Cretaceous, of which traces have been seen in several 

 counties. It indicates also the littoral nature of the Cretaceous beds from 

 which it was derived. 



There is still another indirect evidence of the existence of the Creta- 

 ceous in the western portion of Fillmore county. There are heavy deposits 

 of limonite iron ore, bearing some unascertained relation to the Creta- 

 ceous, or to the drift found in the southwestern part of the county. In 

 the second annual report of the survey mention was made of the occur- 

 rence at a number of places in the Minnesota valley, and in that of the 

 Blue Earth, of a coating of iron ore on the Cambrian rocks where they are 

 unconformably overlain by the Cretaceous. Dr. Shumard says of this 

 (Owen's Geological Survey of Wisconsin, Iowa and Minnesota, page 487): "The 

 nodules of iron ore have mostly a concentric structure, and appear to be 

 of good quality. The superficial indications render it probable that this 

 bed of iron ore may be both extensive and easily accessible." In Fillmore 

 county a discovery was made by Mr. C. C. Temple in digging a well near 

 his sand pit, already described, and referred to the Cretaceous as its prob- 

 able source, which throws some light on the manner of occurrence of the 

 limonite referred to. He testifies that this bed of iron ore /.s- at least thirty -six 

 feet in thickness. In this well, which is six feet in diameter at the top, he 

 dug down about eighteen feet, when he reached rock, fragments thrown 

 out revealing the Galena limestone. He describes the rock as occupying 

 but about one-half of the diameter of the shaft he was digging, which af- 

 forded great quantities of soft limonite or ochre. He drilled into the iron 

 ore a depth of thirty-six feet. A number of wells in the vicinity of Etna, a 

 few miles further southeast, also struck a similar iron ore. On sec. 36, 

 Bloomfield, a great many loose pieces of porous limonite are found in the 

 fields, having been plowed up in the soil. The county surveyor, Mr. J. 

 Gregor, also found it impossible to lay out the quarter sections of that sec- 

 tion in the usual manner, by the use of the magnetic needle, though the 

 original United States surveyors record no disturbance of the magnetic 



