OF ARKANSAS. 135 



GENERAL SUMMARY, INFERENCES, AND REMARKS IN 



CONCLUSION. 



The three leading formations of the northern counties of Arkansas, west 

 of Black river to the Indian boundary, and north of the Arkansas river, 

 are: 



First. The millstone grit, with its associate shales, and conglomerate. 



Second. The subcarboniferous limestone, and its associate chert, shales, 

 and sandstones. 



Third. The magnesian limestones, and their associate sandstones, cal- 

 ciferous sandrocks, and chert, belonging to the lower silurian period. 



The formation known in Kentucky, Indiana, and Tennessee, under the 

 name of the knob sandstone, is absent, or only very obscurely represented. 

 It is doubtful, too, whether the grey and black bituminous shales and 

 slates, belonging to the devonian period, are to be found in Arkansas. 

 There are a few encrinital and variegated limestones and associated chert, 

 which intervene between the magnesian limestones of lower silurian date 

 and the subcarboniferous chert and limestones ; these may belong to the 

 devonian era, but, as yet, I have no positive evidence to decide fully this 

 question. 



No rocks have yet come under observation which I have been able to 

 refer unequivocally to the upper silurian period, such as occur in Jefferson 

 county, Kentucky 1 , Clarke county, Indiana, and elsewhere in these State-. 

 under the coralline beds of the falls of the Ohio. 



East of Black river, in Greene, Poinsett, and Randolph counties, inco- 

 herent sands, loose and cemented gravel, and clays of quaternary date, 

 prevail. 



No crystalline* or hypogene rocks, i. e., no rocks which have been 

 protruded from beneath, as mountain masses, dykes, or veins, possessing 

 the structure of granite or syenite, have been observed, as yet, by the 



* A red granite is reported on Spavinaw creek, near the Cherokee line. Whether this be correct 

 information, I am, at present, unable to say, as I have not examined the locality. 



