38 ECONOMIC BOTANY OF ALABAMA. 



see. Besides certain references in the papers of McCal- 

 ley and Smith just cited, the following describe the bar- 

 rens more particularly: — Mohr 8, p. 88. and the gov- 

 ernment soil surveys of Lauderdale County and the 

 "Huntsville area". 



Geology and soils. — The geological formation of the 

 barrens is mainly the Lauderdale or Keokuk chert, of 

 Lower Carboniferous (Mississippian) age, but the re- 

 gion under consideration is not quite coextensive with 

 that formation. In some places, especially toward the 

 Tennessee line, the larger streams have cut down into the 

 underlying Ordovician limestones. The strata, as in 

 most of the country between the Tennessee River and 

 the Great Lakes, are very nearly horizontal throughout. 

 The soil of the barrens is grayish to yellowish in color, 

 more or less loamy in texture, somewhat more siliceous 

 and much less calcareous than the soils of the Tennessee 

 valley proper, and considered infertile in comparison 

 with them, though it is a considerably richer soil than 

 some in the extreme southern parts of the state which 

 have become very popular in recent years. 



Topography and hydrography. — The surface of the 

 barrens is level to undulating, with ravines or gorges 

 along some of the streams which have cut down into the 

 older rocks as above described. In some of the more 

 level areas there are shallow ponds, bearing considerable 

 resemblance in their vegetation and otherwise to those 

 in some parts of the coastal plain. Streams are moder- 

 ately well developed. 



Climate, — There are no weather stations within this 

 region, but the figures for Madison and Florence, a little 

 farther south, show that the average annual temperature 

 must be about 61°, the length of the growing season 

 about 200 days, and the annual rainfall about 49 inches, 

 most of which occurs in the cooler months. 



Forest types. — In the more level areas a few feet dif- 

 ference in elevation makes a considerable difference in 

 the amount of water in the soil, and consequently in the 

 vegetation. The drier places have forests of short-leaf 

 pines (the pines in this region seem to be almost con- 

 fined to Limestone County, though) and various oaks, 



