THE MISSISSIPPI VALLEY. 329 



mountain masses. Their absolute elevation within 

 the region under consideration, has not been ascer- 

 tained, but is probably in some points little less than 

 8000 feet above the Atlantic ocean. 



The space between 25° and 21° W. is occupied by 

 a red muriatiferous sand stone, containing gypsum, 

 and in many respects closely resembling the sand 

 stone of various rock-salt formations. Rock-salt has 

 not as yet been discovered here, but large masses of 

 chrystallized salt are frequent. 



An arm of the sandy desert extends between this 

 sandstone and the coal strata along the western side 

 of the Ozark mountains in longitude 18° W. 



The secondary deposites about the sides and sum- 

 mits of the Ozark mountains, embrace several exten- 

 sive strata not common to other parts of the basin of 

 the Mississippi. These repose on an inclined sand- 

 stone like that of the Alleghany mountains. Between 

 the ro>: k last mentioned and the granite is interposed 

 a stratum of clay-slate, highly inclined, and resem- 

 bling the primitive clay-slate of Sew England. The 

 granite of thi^ interesting range of hills is, as yet, but 

 little known. It breaks through the superincumbent 

 strata in a valley called the Cove, about fifteen miles 

 south east of the Hot Springs of Washita. 



The western slope of the Alleghany mountains is 

 believed to be nearly similar in character, at the two 

 points contemplated in the sections, except that in 

 the southern the primitive rocks rise to a great eleva- 

 tion, but do not appear in the other. 

 41 



