88 GEOLOGICAL SURVEY OF THE TERRITORIES? 



purpose best. Iu Nebraska the sandstones of the Dakota Group rest 

 directly upon rocks of the age of the coal measures. Although they do 

 not appear in full force until we reach a point near De Soto and beyond, 

 yet remnants of the sandstones make their appearance within five or 

 ten miles of Omaha at any point north of the Platte Eiver. It is quite 

 probable that they once extended all over Nebraska, passing across into 

 Iowa, and how much further eastward we have not definite data to de- 

 termine. The coal-measure limestones are thus exposed in northeastern 

 Nebraska by the erosion of the cretaceous rocks. This is a very import- 

 ant matter in a practical point of view, for the sandstones of the cretace- 

 ous group are seldom of much value for building purposes, and the ex- 

 posure of large areas of the carboniferous rocks in the most fertile por- 

 tions of the State is a fact of inestimable value. 



Fig. i. 



Chalk Bluffs, Cretaceous No. 1, near Blackbird Hill, Nebraska. 



Along the banks of the Missouri Eiver, on the Indian Eeserve, is a 

 lofty escarpment of yellow, rotten, coarse-grained sandstone, sometimes 

 called Chalk Bluffs, from their whitish chalky appearance in the dis- 

 tance. They are from one hundred to one hundred and fifty feet in 

 height, and about half way up, or at least fifty feet above the water, and 

 as much from the top of this perpendicular wall, are carved out numer- 

 ous Indian hieroglyphics, as pipes, canoes, various kinds of animals, rude 

 representations of the Indians themselves, &c. The question at once 

 arises, who carved them here? The Indians now living cannot account 

 for them, and call the rocks " Medicine," a term which they apply to 

 all things that are mysterious to them. The characters closely resemble 

 those on their robes worn at the present day, and are doubtless emblem- 

 atical of some important event in Indian history. These figures must 

 have been carved here many centuries ago, when that portion of the 

 escarpment was accessible from beneath in some way, all trace of which 

 has been effaced by the water. Similar ones are still to be seen in other 

 localities, especially in the mountains. A small creek, which flows into 

 the Missouri a few miles below the " Sunning Water," has an Indian 

 name which signifies " Where the dead have worked," from the fact, 

 that upon the high chalky walls that form its banks are some of the 



