42 ECONOMIC BOTANY OF ALABAMA. 



On account of the prevalence of limestone in the val- 

 ley, caves, natural bridges, subterranean streams and 

 large limestone springs are rather common. The springs 

 are found in every county; the most noted are those at 

 Huntsville and Tuscumbia. 



The Tennessee River, which touches nearly every 

 county in the region, is a large navigable stream, over 

 half a mile wide in some places. Very few accurate 

 measurements of its fluctuations in Alabama are availa- 

 ble, but there are probably places where it rises as much 

 as 50 feet. Its water is very muddy in spring, but green- 

 ish in late fall or whenever it is near its lowest stage, 

 the green color presumably resulting from a mixture of 

 the blue characteristic of limestone streams with yellow 

 clay in suspension. Musself Shoals, in Lauderdale, Col- 

 bert and Lawrence Counties, is a noteworthy feature of 

 this great river. There the river falls 85 feet in about 

 15 miles, over strata of the Lauderdale chert, and is very 

 wide and dotted with numerous islands. Opposite De- 

 catur and at a few other places along the more sluggish 

 portion of the river it is bordered by swamps and 

 sloughs something like those along some coastal plain 

 rivers. 



In Brown's Valley the streams, including the Tennes- 

 see itself, all run lengthwise of the valley, except in 

 Blount County, where they run out of it into the adjoin- 

 ing coal region, as do some of those in the Coosa valley 

 region. 



Climate. — Climatic data for the Tennessee valley can 

 be found in the appendix, under the stations Madison, 

 Decatur and Florence. The winters are damp and the 

 summers dry, as a rule, which together with the fluctua- 

 tions of the Tennessee River must cause considerable sea- 

 sonal variations in the ground-water level, and facilitate 

 the natural processes of soil formation. 



Forest types. — The forest types of this region are as 

 diversified as the topography. It is difficult to recon- 

 struct in the mind's eye the original forests of the fertile 

 plain bordering the river, but they must have been large- 



j-Often misspelled "Muscle." 



