432 THE OOLOGY OF MINNESOTA. 



[Cretaceous beds. 



formed in the Cretaceous age. Similar formations, containing character- 

 istic Cretaceous fossils, occur in other portions of this state, toward the 

 east, north and west, and have a great development farther west in the 

 region drained by the upper Missouri river. No fossils have been found, 

 however, in any of these deposits in this county, though they are exposed 

 in many localities and present much diversity in material. They often 

 occur in the ordinary manner of stratified sediments, unconformably over- 

 lying eroded surfaces of the Jordan and Shakopee formations; but another 

 frequent mode of occurrence is in large water-worn cavities and fissures 

 of these rocks, principally of the Shakopee limestone. Before the deposi- 

 tion of the beds here called Cretaceous, these Cambrian rocks at many 

 places in the Minnesota valley had become channeled by rivers and sculp- 

 tured into irregular basins, pot-holes, and hollows, from five to twenty-five 

 feet in depth, often partly covered by overhanging walls. These pocket- 

 like cavities are smoothly water-v/orn, and their surface is often thinly 

 coated with iron ore. Within them clay has been sifted and packed so 

 as to fill their irregular spaces, frequently covered in part by the limestone. 

 The crust of iron ore Qimonite with a little manganese oxide) was probably 

 formed, however, since the clay was deposited. It should be added that 

 the clay was doubtless of greater depth and extent at some former time; 

 so that all the ore-covered surfaces observed may have become thus en- 

 crusted while enveloped in the clay. This deposit is, more strictly speaking, 

 a very fine sandy and clayey silt, greenish or bluish, weathering white, hori- 

 zontally bedded, or conforming somewhat to the shape of the hollow that 

 holds it. 



The following descriptions of these Cretaceous beds are given in geo- 

 graphic order, as they are found in descending the Minnesota valley, and 

 afterward their exposures on the Blue Earth, Watonwan, Le Sueur, Maple 

 and Big Cobb rivers are successively noted. 



Within the Minnesota valley, in this county, the first occurrence of deposits probably of 

 Cretaceous age is on land of Edward Howe, in the west part of section 23, Cambria, where a con- 

 glomeritic sandstone, much broken into masses of various sizes up to eight or twelve feet long 

 and five or six feet thick, covers a small area beside the river, having about the same hight with 

 the flood-plain. It is underlain by a fine blue clay, without gravel or pebbles. Comparing these 

 with the other beds of similar character in this region, we find outcrops of the sandstone on the 

 opposite side of the river, in Nicollet county, one mile below and about two miles above this 

 point. At the second of these localities some of its layers contain fragments of wood, or lignite, 

 and aiigiospermous leaves. The underlying clay appears to be the same with that which else- 



