county across the State, widening out into a broad belt of country in Southwest Georgia. The country abounds in lime-sinks and in some sections in small lakes -lime-sinks filled with water. The whole country is full of depressions or sinks, in many places giving only a slight inequality of surface, that of a network of low ridges -a sort of honey-comb topography in low relief.

This is a country of subterranean streams. The surface drainage is not generally good. The water that falls must find its way either through open sink-holes, or else by filtering through the soil, into the under-ground channels. The marl beds found at depths of from twenty to fifty feet is the water-carrying stratum of the country. Some of these under-ground waters find outlets in bold limestone springs. These are more common along the south west border of the lime-sink belt. The general direction of the streams, as shown by the lines of sinks, conform to the southern or southeastern inclination of the strata and to the general direction of the surface drainage in South Georgia. Ponds, lakes and swampy lands have been successfully drained by boring through to the marl beds, allowing the water a ready escape into under-ground channels.

Kind of Rocks. The formation is largely made up of sandy layers alternating with clays and calcareous marls or limestones. Most of these exist in a soft or friable condition. The marls or limestones; the Buhrstone; a feruginous sandstone, in thin layer occurring about the upper border of the formation, and the buckshot concretions, before mentioned, are, nearly the only rocks of sufficient hardness not to crumble in the hand, or break down on exposure.

The Buhrstone is found near the upper limit of the lime-sink belt, and is itself a silicefied portion of the marl beds. This stands out in bluffs on some of the streams. Some fine exposures of the bed are found on the Savannah river in Scriven county. It does not appear to extend across the State in a continuous bed, as do the marl beds, but is found with interruptions along its northern limit, as shown by the Mineral Map of the State.

QUARTERNARY.-At the close of the tertiary remarkable changes took place in the climate of the earth. A large part of the northern hemisphere was covered with glaciers, and arctic animals were driven by the extreme cold into the temperate and semi-tropical regions. The effects are observed in the drift of high latitudes-transported materials, such as sand, clay and rounded boulders, with

which the country is covered as far south as Pennsylvania and Ohio. From this phenomenon the first part of the Quarternary is designated by the name of the Glacial Period or that of the Drift or Ice Age. This was succeeded by the Champlain Period and the Recent or Terrace Epoch.

The melting of the glaciers as the closing event of the Ice Age brought on a flood of waters and gave rise to a flood-made deposit, covering with sand and pebbles the older formation in some parts. of the Mississippi Valleys. A deposit of sand and pebbles along the upper border of the Tertiary in Georgia has been thought by some geologists to have had a like origin.

The low hammock lands, the estuary and delta formations near the coast and the alluvium of streams, the swamp muck and stalagmetic cave deposits in all parts of the State, as well as some local drifts in the coves and at the mouth of mountain ravines, belong to this age.

CHAPTER VI.

AGRICULTURAL GEOLOGY.

Under this head, the several geological formations of the State will be dealt with in their agricultural relations.

Soils have their origin in the decay and disintegration of the rocks, and where a soil rests on the stratum from which it is derived, it is always closely related to this in composition. Some soils, however, are brought in part or entirely from a distance, and may have their sources in the wearing down of rocks wholly different from the ones on which they rest. These are transported soils. The alluvial deposits, the material of which is derived from the diverse strata traversed by the streams, is generally of this character. There are no extensive areas in Georgia, as in some of the Northern States, covered with drift material brought from remote localities. The soils of the State elsewhere than in the alluvium of streams, with rare exceptions, are derived either from underlying rocks, or else from immediately adjacent groups.

In crossing the country northwest and southeast, in Northern and Middle Georgia, frequent well marked changes in the soil and growth of timber are observed that point with much certainty to corresponding changes in the underlying rocks.

In the account given of the soils of the State in the following pages, reference is made to the geological groups to which these belong, and which are described more in detail on preceding pages.

NORTHWEST GEORGIA.*

The following table gives the geological divisions that are represented in this region, and also the thickness of each group. The lithological features of each group varies somewhat in the eastern and western sections, and it is of sufficient interest to represent this in the list by making Taylor's ridge (a prominent and sharptopped mountain chain in the middle of the region) a dividing line and in the two columns showing the features of each group.

*The descriptions here given of the soils of this part of the State are extracted from Professor Hilgard's Report on Cotton Culture, published in Vol. VI, 10th Census. This was prepared from geological notes and maps now in the office of the Department of Agriculture.

NOTE.-The groups that afford arable lands are in italics; the others in general enter into the structure of steep mountains and

ridges.

The soils of the different groups are well characterized, each affording one in many respects peculiar to itself. For this reason it will be most convenient to consider separately the soils of the formations that give rise to arable lands.

The following comprise the chief varieties:

1. Brown and red loams. 2. Gray siliceous soils of the ridges. 3. Sandy table or mountain lands. 4. Flatwoods. 5. Alluvial lands.

BROWN AND RED LOAMS.

These are formed from the limestone and calcareous shales of several geological formations, and, as they differ somewhat, they are described separately.

Lands of the Chazy and Trenton.-The lands are highly calcareous, and are perhaps the richest uplands in the State. The timber is. large, and consists principally of red. Spanish, and white oaks, hickory, poplar, sugar maple, post, oak and cedar, with an admixture of other varieties common to the country. The lands generally lie well, but when hilly are inclined to wash. Where the limestones are nearly horizontal, these are sometimes exposed, or else lie in close proximity to the surface. Such lands are usually covered with a growth of cedar and red haw, and are known as cedar glades; but there are no very extensive areas of this kind. Where the limestones lie unexposed near the surface, this fact is usually indicated by a growth of post oaks.

The soil consists of two principal varieties, viz., a brown calcareous loam of the blue limestone areas and red calcareous loam of the rotten limestone.* The first varies in color from a light to dark brown and almost black, a dark or chocolate brown being the most characteristic color, with a subsoil approaching to red. The soil of the rotten limestone belts is a dark red color with a red subsoil. There is a striking difference in the appearance of these lands, though in the more essential characteristics of productiveness and in adaptation to various crops there is little difference. Lands that have been in cultivation for thirty or more years will often produce from 30 to 50 bushels of corn to the acre. The soils seem to be considerably deteriorated for the wheat crop, but when rested in clover, and the crop turned under, from 10 to 20 bushels is not an unusual yield. Cotton has been grown but little on these lands north of Floyd county, and in this county and Polk about 600 pounds of seed cotton per acre is the usual yield.

Subcarboniferous brown loam lands. The rocks of this formation

*The blue limestone areas are on the eastern and the western sides, and the rotten limestone in the central part of this division of the State.