hayes and kckel.; IRON ORES OF CARTERSVILLE DISTRICT, GA. 239 
to sea level, and in its lower portions, chiefly those underlain by the 
Chiokamauga limestone (the next formation above the Knox dolo- 
mite), swamps were formed which received drainage from the 
adjacent regions, and in which extensive deposits of bog ore were 
formed. When the region was elevated, the limestone areas were 
again reduced more rapidly than the adjacent areas underlain by 
dolomite, and doubtless much of the accumulated iron ore was 
removed by erosion. Around the margins, however, the ore remained 
embedded in the residual clay. Deposits of this character are 
especially abundant in the Rockmart and Cedartown districts, south- 
west of the Cartersville area. These districts comprise a number 
of areas of Chickamauga limestone, surrounded by zones which 
contain large quantities of iron ore. This is usually in the form 
of gravel ore, composed of concretions from the size of shot up 
to a foot or more in diameter, embedded in the residual red clay, 
and associated with more or less chert from the underlying Knox 
dolomite. 
3. The brown hematites of the third class, here called concentration 
deposits, constitute the most important deposits of the Cartersville 
district. They may occur wherever a limestone is underlain by an 
insoluble and impervious stratum, such as sandstone or quartzite. 
Favorable conditions for this accumulation occur in northwest Geor- 
gia and Alabama, at the contact of the Lower Carboniferous lime- 
stone with the sandstones which sometimes underlie it, and at the 
contact of the Beaver limestone with the underlying Weisner quartz- 
ite. The Beaver limestone is more readily soluble than the forma- 
tions on either side, and hence, in the erosion of the region, it has 
always formed valleys. At various times these valleys have received 
the drainage, not only from the adjacent quartzite and limestone, but 
probably also from other of the valley formations, and the widely dis- 
seminated iron leached from these formations during the process of 
decay has been transported to the limestone valley and there concen- 
trated upon the underlying impervious quartzite. As the surface of 
the limestone was lowered, chiefly by solution, upon successive eleva- 
tions of the region, remnants of the ore deposits thus formed were left 
resting upon the underlying quartzite and marking elevations at which 
the surface of the limestone had remained for considerable periods. 
These deposits are composed in part of gravel ore and in part of 
masses of considerable size, in some cases reaching many feet in diam- 
eter. Where the large masses of ore preponderate, it is probable that 
they represent replacements of the limestone by iron-bearing solutions 
rather than ordinary bog-ore deposits. When the deposition was by 
direct replacement of limestone below the level of ground water, the 
iron was probably in the form of carbonate, changing to limonite as 
the ground-water level was gradually lowered with the progress of 
erosion. At a few points the limonite deposit has been traced down- 
