COOS A AND TENNESSEE VALLEYS. 21 



REGION OF THE COOSA VALLEY. 



Between the region of crystalline rocks and the region of the Coal 

 Measures a narrow area inserts itself, extending in a southwesterly 

 direction along the course of the Coosa River for a distance of about 

 50 miles, located upon the line of the greatest disturbance caused by 

 the Appalachian upheaval. Consisting of an anticlinal valley, the river 

 valley proper, and a succession of vertically uplifted strata of Cam- 

 brian and Silurian rocks with successive faults, the surface of this 

 region is extremely broken and presents a mountainous aspect. To 

 the southeast of the anticlinal, through which the river winds its way, 

 the hard Lower Cambrian sandstone, offering the greatest resistance 

 to the action of water, forms the most prominent ridges in the Alpine, 

 Coldwater, and Ladiga mountains, reaching a height of from 1,800 to 

 2,000 feet above the sea. The upper aluminous strata of the Cam- 

 brian shales cover the floors of the valleys, where from want of drain- 

 age they give rise to the stiff impervious clay soils of the "flatwoods." 

 Areas of these flatwoods are found in the anticlinal valley itself, which 

 is for considerable distances covered by drifted sands and gravels. 

 Where the cherty beds of the Silurian dolomite prevail, the surface 

 in the valleys is more or less broken and the soil thin. The surface 

 soil of the Coosa Valley along the banks of the river (i. e., in St. Clair 

 County) is underlaid by the Subcarboniferous shales. 



Running mainly parallel with the Coosa Valley and similarly inter- 

 secting the Coal Measures there are several smaller valleys similar 

 to the Coosa Valley proper in their geological and topographical 

 conditions. 



REGION OF THE TENNESSEE VALLEY. 



The remainder of the northern part of the State north and west of 

 the Coal Measures is covered by the strata of the Subcarboniferous 

 formation, which form the region drained by the Tennessee River. 

 The river basin is about 45 miles wide, and toward its northern and 

 southern limit is hilly, and often even mountainous. The plain 

 through which the Tennessee River winds its tortuous way is from 12 

 to 15 miles wide. On the western frontier of the State the river level 

 is about 480 feet above tide water, while near Huntsville it reaches an 

 elevation of 612 feet. 



West of the table-land of the Cumberland Mountains, already 

 spoken of in connection with the Coal Measures, this plain or valley 

 proper is bounded by the Highlands of Tennessee, described as a 

 plateau of from 700 to 800 feet above the sea, through which numer- 

 ous streams have cut their deep and narrow channels, rendering the 

 surface very broken and hilly. South of the river the escarpment of 

 the Sand Mountain forms the southern boundary of the valley. From 

 the eastern part of Morgan County in a northwesterly direction the 



