346 DRAKE — THE GEOLOGY OF IXDIAX TERRITORY. [Sept. 3, 



are called St. Clair marbles. These beds are underlain by blue and 

 gray limestones called the Izard limestone. The Izard limestone 

 is underlain by saccharoidal sandstones, magnesian limestones and 

 cherts. 



All the Silurian deposits seen in the Indian Territory, except the 

 Salisaw and Elk creek areas, are composed of saccharoidal sand- 

 stones, cherts and calcareous, magnesian sandstones. The Salisaw 

 and Elk creek Silurian rocks, however, are mainly pink and gray 

 marbles, and therefore appear to be the equivalent of the St. Clair 

 marble, while the Illinois river and Spavinaw creek areas belong to 

 the beds below the Izard limestone. 



The St. Clair marbles in Arkansas are principally confined to 

 Independence, Izard, Stone and Searcy counties, in the northern 

 part of the State. The Izard limestones have a somewhat wider 

 range,^ but neither the St. Clair marble nor the Izard limestones 

 are known as far northwest as Benton county, Ark.,^ or to the west 

 of Benton county, in the Indian Territory. So it appears that 

 these topmost Silurian beds were eroifed in the northwest to a 

 greater extent than they were to the south and east, before they were 

 covered by later deposits. Dr. Henry S. Williams,' principally 

 from biological investigations, has determined the top of the St. 

 Clair marble to be of Clinton-Niagara age, and the lower part of it 

 to be of Trenton age. From the thickness of the marble beds in 

 the Salisaw creek areas, as shown by drill holes, it is probable that 

 the outcropping part is the equivalent of the Clinton-Niagara part 

 of the St. Clair. 



Lower Carboniferous. 



Area. — The Lower Carboniferous is confined to the northeast 

 part of the Cherokee Nation and is roughly bounded on the west by 

 the Grand or Neosho river and on the south by the Boston moun- 

 tains. This area covers about three thousand square miles, approxi- 

 mately one-half of the Cherokee Nation. 



Lithology. — The rocks composing the Lower Carboniferous are 

 cherts, limestones, shales and sandstones. 



Structure. — The beds as a rule are practically horizontal, especially 

 in the northeastern part of the area. Along the western border of 



^Ann. Kept. Geol. Stir. Ark., 1890, Vol. iv, p. 112. 

 "^ Ann. Rept. Geol. Sur. Ark., 1891, Vol. ii, pp. 27-32. 

 "^ Am. Jour. Sci., 1894, Vol. cxlviii ]■)]). 32S, 329. 



