Assodation of American Geologists and Naturalists. 129 



formations above the disturbed strata just referred to, in conformity to 

 each other. The distance between these two points is three hundred 

 and fifty or four hundred miles. The thickness of the formations here 

 is very small when compared with those of the Alleghany region. 

 Hence the basin-like curve between these points is not great, giving the 

 appearance of almost horizontality within moderate limits. 



The lower portion of this basin consists of an immense deposite of 

 magnesian limestone ; the upper, of the limestones, sandstones, shales, 

 and coal of the great western coal basin. The magnesian limestone 

 deposite is subdivided by a well marked deposite of siliceous sandstone, 

 generally light-colored, often perfectly white and friable. The lower 

 division of the magnesian limestone is light brown, or ashy in color, 

 very compact or hard, but decomposing with considerable rapidity when 

 exposed to atmospheric or aqueous influences. In Missouri it presents 

 many interesting views of precipices, caves, natural bridges, &c. At 

 Prairie du Chien it rises about one hundred feet above the level of the 

 river, but in Missouri, in the vicinity of Eangua River, it rises much 

 higher. Although it resembles the upper division very much in litho- 

 logical character, it differs entirely, so far as it has yet been explored, 

 it being totally deficient of fossils and nearly or quite so of valuable 

 minerals. Its entire thickness has never been determined. As there 

 are reasons to believe that it belongs to a distinct geological epoch, and 

 as an important economical purpose will be served in discriminating 

 between it and the upper division. Dr. King proposed to call this the 

 Eangua limestone ; this name being of course only provisional, and 

 expected to yield, if on further investigation of the connexion between 

 this and the Appalachian region it shall be found to be only a continu- 

 ation of one of the latter series, or when a satisfactory systematic no- 

 menclature shall have been adopted by American geologists generally. 



Above this division of the magnesian limestone deposite, lies the sand- 

 stone already referred to, and which appears rarely to exceed fifty feet 

 in thickness. It is remarkably uniform, being almost identically the 

 same in thickness and lithological character at Prairie du Chien that it 

 is in the southern part of Missouri. Above this, in Wisconsin, is a de- 

 posite of limestone, in strata of various thickness, making in all about 

 twenty or thirty feet, remarkable for the abundance of the fossils, for its 

 containing the seams of a brown coal-like matter, and for its marked 

 difference in lithological character from the magnesian deposits above 

 or below. Dr. King did not find this fossiliferous limestone in Missouri, 

 though he was not prepared to deny its existence there. Judging from 

 the ingenious tracings of the New York formations westward by Mr. 

 James Hall, Dr. K. was willing to admit the high degree of probability 

 . Vol. XLvii, No. 1.— April-June, 1844. 17 



