282 F. H. Bradley—Silurian age of the Southern Appalachians. 
is often very perfect throughout large masses. This structure 
of lead and zine ores, the weathered portions of the latter 
showing much calamine and smithsonite. Barite is also quite 
abundant, though often impure. Fluorite also occurs in small 
quantities. These mainly occur at the filling of cavern-like 
chambers irregularly following the “joints” of the strata; but 
little is yet known of their extent, and nothing as to any law of 
their distribution. They also occur in grains disseminated 
through the mass of the ‘Tock. The most abundant ore along 
the outcrop of this series is limonite, which occurs in immense 
beds, both compact and ochreous. It is plainly a surface 
others are almost entirely free from such impurities. Most o 
this ore contains more or less eg apes ore, partly in the form 
of wad, partly as psilomelane. The very general var aacaRy le 
of iron through the limestone, as sulphide, as oxyd, or as 
lama is evidenced by the color of the fare beds of readin 
own clay accompanying every outcrop, which have been 
cue, from the impurities of the rock, as the lime and magne- 
sia salts have been dissolved away. 
* These immense beds of debris, along the outcrops of all but the very hardest 
and most siliceous rocks, are the constant characteristic of all this southern region, 
charge was by the valley of the Coosa River, directly to the Gulf of Mexico. 
stead of by the present valley of the Tennessee. The Clinch must then zane 
formed the main source of the laeoegor ds = possibly this may also have found 
@ sout ainaeern 0 utlet after passing 
The — ——— of the rag will also account for the entire absence of 
lakes in region, since any body of water, if ever crgre ing here, would find nat 
wn i most 
