COASTAL PLAIN AND REGION OF CRYSTALLINE ROCKS. 19 



Tertiary formation, slightly dipping south and southeast. The warm, 

 fertile, calcareous soils nvsulting from admixtures of these strata with 

 the Lafayette loams support an arboreal ^'eg•etation of varied char- 

 acter. The lower members of this formation, Buhrstone strata, con- 

 sisting of hard, flinty limestones, render the surface of the plain 

 broken by cherty hills which rise above the underlying lignite marls. 

 Further north these hills merge into the cretaceous plain, or " Black 

 Belt," so called on account of the })lack lime soil, the great agricul- 

 tural region of the State. This Black Belt is followed by a belt of 

 gravels and sand, partly of the lowermost Cretaceous (Tuscaloosa) for- 

 mation, partly of the Lafayette formation, in which sandy loams pre- 

 vail, and which is from 5 to 30 miles in width, widening at its western 

 border, where it suddenly takes a northern direction and forms the 

 geological feature of that section of the State to the Tenn(\ss(^e River. 

 This central belt of sands and pebbles forms the northern border of 

 the great Coastal plain, separating the Paleozoic from the Mesozoic 

 formations. Through its southern portion runs the border line between 

 the two principal biological divisions of the State, the Austroriparian 

 or Louisianian life area and the Carolinian life area (Merriam). 



North of this Coastal plain rise the highlands of Alabama with their 

 mineral wealth, which cover about two-fifths of the area of the State. 

 The first terrace of this mountainous region forms the so-called "Fall 

 line." Here the head of river navigation is reached, the tri})utaries 

 of the Tombigbee and Alal)ama in this region making their way over 

 rocky obstructions, over shoals and through rapids, to the main chan- 

 nels of the extensive drainage area south of the Tennessee River. 



Rl^GION OF CRYSTALLINE KOCKS. 



Ascending this terrace at the falls of the Tallapoosa River, the most 

 easterly of the tributaries of the Alabama, the region of crystalline 

 or metamorphic rocks is reached. This extreme southern extension 

 of the eastern Appalachian ranges consists of a congeries of crystal- 

 line rocks, to a small extent granitic, mostly of stratified gneiss, 

 micaceous schists, argillaceous shales, and quartzites, wrinkled by 

 many folds and deeply furrowed by the effects of erosion. The 

 difierent degrees of resistance to this agency offered by these various 

 rocks give rise to an ever-changing configuration of the surface, 

 and to wide variations in the mechanical and chemical conditions 

 of the soil. The folds of the highly siliceous slates and (luartzites 

 form sharp crested ridges of an elevation not reached in any other 

 part of the State, while the stratified gneissic rocks and clayey 

 slates most prone to decay under atmospheric influences form the 

 undulating uplands. The sandy soils derived from the first men- 

 tioned siliceous rocks, often intermixed with the angular fragments of 

 quartz and hard slates, render the surface obdurately sterile: while 



