COASTAL PLAIN AND REGION OF CRYSTALLINE ROCKS. 19 
Tertiary formation, slightly dipping south and southeast. The warm, 
fertile, calcareous soils resulting from admixtures of these strata with 
the Lafayette loams support an arboreal vegetation 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 black 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 Tennessee 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 itssouthern 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 tributaries 
of the Tombigbee and Alabama 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. 
REGION OF CRYSTALLINE ROCKS. 
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 
different 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 quartzites 
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 
