46 GEOLOGICAL SURVEY OF THE TERRITORIES. 



the great geographer, Eitter, says that the grade at which it is possible 

 for earth to cliug is 4oO. At Tekama are some exposures of the sand- 

 stones of the Dakota group, but mostly so soft and friable as to be of 

 little value as building-material. 



In the absence of all other rocks the inhabitants quarry out the harder 

 portions and use them. Underneath the sandstones are the usual vari- 

 egated clays and sands, red, white, gray, and drab, with nodules of the 

 sulphuret of iron. In the sandstones above there is quite a variety in 

 the texture of the rock. Sometimes there are thin intercalations of 

 clay; then little pockets, as it were, of clay inclosed in a thin shell of 

 iron ; then the thin layers are oblique, as if the waters in which the 

 sands were deposited were in currents, or in a disturbed condition. 

 Indeed, it would hardly be possible to describe all the varied conditions 

 which this rock presents. Between Tekama and Decatur, a distance of 

 about sixteen miles, there are frequent exposures of the sandstones and 

 clays, but none worthy of special notice until we reach the vicinity of 

 the little town of Decatur, near the border of the Omaha reserve. 

 Here some harder layers of rock are exijosed, which are used for the 

 foundations of buildings and other economical purposes. There is one 

 layer of quartzite. 



There are also thin seams of iron-ore, which, when broken with a 

 hammer, give forth a sound much like that from old pot metal. It m 

 really pretty fair iron-ore, but quite siliceous and impure, and even if 

 this ore was of the best quality, and in great abundance, there is no 

 fuel in the county to render it of any value. 



At the Blackbird Mission, on the Missouri, eight miles above Decatur, 

 the bluffs of sandstone are quite conspicuous, and often present very 

 high mural fronts, upon which the Indians have carved many rude pic- . 

 tures, doubtless portions of their hieroglyphical history. At this locality 

 are quite numerous layers, from one to four feet thick, of a very com- 

 pact massive quartzite, the hardest and most durable rock in the State. 

 It has the appearance of a metamorphic rock, so very hard and close- 

 grained is it. The harder portions have been quarried out and used 

 for the construction of a very large three story building for the mission 

 school. 



As the construction of several railroad-bridges across the Missouri 

 are contemplated, no rock in the State would be so unyielding and 

 durable for abutments as this, providing enough of it can be fouud. It 

 seems to assume a concretionary form in the sandstone, and is of very 

 uncertain thickness and extent. 



About two miles above the mission the hills are cut by the river so as 

 to reveal vertical bluffs, the rocks of which, in the distance, have a yel- 

 lowish-white appearance, aud from this fact are usually called chalk-bluffs. 

 The sandstone is massive, almost without stratification, and very friable 

 and soft. 



4. Yellow marl ; recent ; ten to fifty feet. 



3. Eight inches of earthy lignite resting upon twelve inches of yel- 

 lowish-drab arenaceous clay, underlaid by eight inches impure lignite. 



2. Massive yellow standstone, with some thin intercalations of clay, 

 soft and friable, readily yielding to the erosive effects of Avater, sixty to 

 eighty feet thick. 



1. Yellow plastic unctuous clay, toward the top becoming a grayish 

 blue ; contains flat argillaceous concretions two feet. 



This is, perhaps, the finest and largest exposure of the rocks of this 

 group along the river. The mural exposures of soft sandstone present 

 good surfaces for the Indian to make use of on which to wTite his rude 



