The Position of the Cincinnati Grotip. 113 



The coal measures are 14,570 feet thick in Nova Scotia (Acadian 

 Gcio., p. 177), 8,000 feet in Pennsylvania, 2,000 feet in Ohio, 2,500 feet 

 in Tennessee,; 1,200 feet in Illinois, 640 feet in Missouri, 2,000 feet in 

 Kansas, and a greater thickness westwardly, in Nebraska, 



The maximum thickness, therefore, of the carboniferous rocks is 

 23,606 feet, or nearly four and one half miles. 



The Triassic and Jurassic formations have been variously estimated 

 as to thickness in several western territories. There can be no doubt, 

 however, that, at the maximum, 3,000 feet of these rocks intervene be- 

 tween the carboniferous and cretaceous rocks, as will be seen from the 

 report of Prof. Newberry, geologist to Ives Colorado Expedition, 

 Hayden's Reports on Montana, Wyoming, etc., and the Geological Re- 

 ports of the Pacific R. R. Survey. 



The Cretaceous Group is subdivided in Tennessee in the ascending 

 order, into : 1st, Coffee sand ; 2d, Green sand, or shell bed ; 3d, Ripley 

 Group. The Coffee sand takes its name from Coffee Bluff, or a sup- 

 posed resemblance in color, and is 200 feet in thickness. The Green 

 sand takes its name from the green grains found in it, and is 350 fee 

 thick. The Ripley Group is 500 feet in thickness, making the maxi- 

 mum depth in Tennessee 1,050 feet. (Geo. of Tenn., p. 165.) 



It is subdivided in Mississippi, Alabama, and Louisiana, in ascend- 

 ing order, into : 1st, Eutaw Group ; 2d, Tombigbee sand ; 3d, Rotten 

 limestone ; 4th, Ripley Group. The Eutaw Group takes its name from 

 Eutaw, Alabama, and is about 400 feet in thickness, and is the equiva- 

 lent of the Coffee sand of Tennessee. The Tombigbee sand takes its 

 name from the river of that name, and is about 100 feet thick. The 

 Rotten hmestone is about 1,200 feet in thickness, the Ripley Group is 

 about 350 feet thick. Making the total thickness in tliese States 2,050 

 feet. 



The Cretaceous Group is, however, much thicker than this on tlie 

 great plains west of the Mississippi, where 3,000 or even 4,000 feet 

 will probably not be an overestimate. 



The Tertiary Group of Mississippi, Alabama, and Louisiana, is di- 

 vided in ascending order, into : 1st, Northern Lignitic ; 2d, Claiborne 

 Group ; 3d, Jackson Group ; 4th, Vicksburg Group ; 5th, Grand Gulf 

 Group. The maximum thickness of all is about 1,500 feet. The 

 Tertiary, on the Alantic coast, falls far below this maximum, but it 

 exceeds it in Texas and the western territories. The Miocene strata 

 alone, of California, is 2,211 feet in thickness, and Prof. Blake estimated 

 the total thickness of the Tertiary series of strata in that State at 

 not less than 3,000 feet. On the coast range of mountains the Tertiary 

 is supposed to be the thickest of any part of the continent, and to 

 much exceed 3,000 feet. 



