GEOLOGICAL SURVEY OF THE TEERITOEIES. 19 



of rock are horizontal or nearly so. Indeed, it is very seldom that the 

 beds incline to such an extent as to be perceptible to the eye. That 

 there is a general inclination of the beds to the west or northwest is 

 evident, but it is very gradual. This yellow-marl deposit, or bluff" forma- 

 tion, as it was called in the geological report of the State of Missouri, is 

 found largely developed in the valley of the Missouri, and extends from 

 its mouth to the foot of the great bend above the mouth of White Eiver. 

 This deposit was first noticed by Sir Charles Lyell in his visit to this 

 country in descending the Mississippi many years ago, and he regarded 

 it as the equivalent of the Loess of the Ehiue. It is called the " bluff 

 formation," because it forms the picturesque hills or bluff's which are 

 seen along the Missouri Eiver, especially on the Iowa side, between 

 Council Bluffs and Sioux City. This deposit was accumulated just prior 

 to the present period, after the surface had received its present outline 

 by erosion, and after the great valley of the Missouri had been carved 

 out. It would appear that one of the comparatively recent geological 

 events was the settling back of the waters of the Gulf of Mexico by a 

 depression of all this western country in such a way that there was a 

 vast fresh-water lake, extending up the valleys of the larger streams for 

 a considerable distance into the interior of the country, generally not 

 more than from 50 to 130 miles. Its greatest thickness is along the 

 Missouri River, where it is sometimes seen in vertical exposures from 50 

 to 150 feet in thickness. Sometimes the stratificatiou is quite distinct ; 

 but, as a rule, no lines of deposition are visible, showing that the mate- 

 rials were brought down into the lake by the myriad little streams, and 

 mingling with the waters of the lake settled to the bottom quietly like 

 gently-falling snow. In the drift or gravel deposit underneath are abun- 

 dant exhibitions of turbulent waters, but never in the yellow-marl beds. 

 All of this marl is full of nutritious matter for vegetation, and it is proba- 

 ble that it is to this deposit that the inexhaustible fertility of all the 

 river counties of Nebraska may be attributed. 



Upon this marl rests the soil, which is usually darker colored, and is 

 composed largely of humus arising from the annual decay of a luxuriant 

 growth of vegetation. The soil on the upland is usually from twelve to 

 eighteen inches thick, and along the bottoms of streams is sometimes 

 ten to twenty feet in thickness. In the yellow-marl formation are found 

 numerous shells, all identical with recent species, and most of them liv- 

 ing in the vicinity. This shows the modern character of the deposit. 

 There are also some bones of extinct animals, as the mastodon, elephant, 

 a species of beaver of huge dimensions, and other animals, mingled with 

 bones of species now living. Along the Missouri the bluff's formed by 

 this deposit are very steep, and I have seen vegetation growing upon 

 them when the sides had an inclination of fifty degrees. These hills, 

 although furnishing good grass, cannot be devoted to the raising of the ce- 

 reals ; but, as the soil is chemically about the same as that of the Loess 

 of the Rhine, which makes that Valley one of the finest vine-growing 

 countries of Europe, the same may be inferred of this region, and it is 

 my belief that at some future period these marl- hills will produce some 

 of the finest vineyards in America. 



Erratic blocks or bowlders are most abundant along the river, yet a 

 few are found from time to time half buried beneath the surface. They 

 reveal the fact at once to one acquainted with the rocks of Nebraska 

 that they are foreigners and were transported from Dakota, Minnesota, 

 or the country bordering upon the Rocky Mountains. Many of them 

 are red quartzite, comparatively little worn, but now and then are seen 

 masses of the different varieties of granite, gneiss, hornblende, &q., which 



