46 GEOLOGY OF ILLINOIS. 



colored soil, about a foot in thickness, which may represent the Post Tertiary 

 soil, penetrated in the shaft, at Coatsburg, underlying the Drift deposits. 

 Here the true Drift is wanting, and the Loess directly overlies these older 

 Post Tertiary beds. Notwithstanding the unsolidified character of this deposit, 

 it is sufficiently coherent to present a vertical cliff where it is intersected by 

 artificial cuts, and often remains for years in nearly perpendicular walls, where 

 it has been cut through by running streams, or in grading the streets of the 

 cities that have been built upon it. It is, everywhere, a fine sedimentary accu- 

 mulation, and usually contains numerous terrestrial and fresh water shells, 

 which, notwithstanding their fragile structure, are found entirely perfect, 

 showing that they have not been subjected to any violent movements before 

 they were buried in the marly sands of this formation. The remains of the 

 Mammoth, Mastodon, Megalonyx, Casteroides, and other extinct animals, 

 occur in the Loess, indicating that it is a deposit formed in a fresh water lake, 

 into which the bones of land animals, and the shells of terrestrial molluscs, 

 were swept by the streams running into it from the adjacent land. The term 

 "Loess," was originally applied to a similar formation, which caps the bluffs 

 of the river Rhine, in Germany, and has been generally adopted by American 

 geologists to designate beds that are similar in their character and origin, to 

 those on the Rhine, and that appear to have been formed at about the same 

 time. 



Drift. This formation is composed of yellowish, brown or blue clays, with 

 sand, gravel, and large boulders of water-worn rock, the whole mass usually 

 showing little or no trace of stratification, and ranging in thickness from thirty 

 to eighty feet or more. It is a heterogenous mass of the water-worn fragments 

 of all the stratified rocks that are known to occur for several hundred miles to 

 the northward, embedded in brown or blue clays, and most of the large bould- 

 ers which it contains, are derived from the metamorphic sandstones, granites, 

 sienites, porphyries, and other metamorphic and igneous strata that occur on 

 the borders of the great lakes. Associated with these, there are also rounded 

 boulders, usually of smaller size, derived from the stratified rocks of this and 

 the adjacent States. Fragments of native copper, galena, coal and iron ore, are 

 often intermingled with the general mass, but are not indicative of mines of those 

 minerals in the immediate vicinity where such fragments are found, for they have 

 been transported from other localities by the same powerful agencies to which 

 the Drift formation owes its origin. The coal shaft at Coatsburg penetrated 

 the thickest bed of Drift that has. perhaps, been found in this county, and I am 

 indebted to Mr. Joseph Edwards, for the following section of the beds passed 

 through in sinking this shaft : 



FEET. IN. 



Soil and yellowish clay . 6 00 



Bluish colored clay and gravel . 45 00 



