152 GEOLOGICAL SURVEY OF ALABAMA. 
and we find throughout the region formed both by the 
Dolomite and the upper partof the Shale, beds of the brown 
iron ore or limonite, which plays so important a part in the 
economic history of all this region. The iron ore seems to 
have been derived from these older rocks. As instances of 
the occurrence of limonite banks connected with the Dolo- 
mite and Shale, I may mention the Edwards Ore Bank near 
Woodstock, the mines at Greely and Goethite, in Jones’ 
Valley, and the great beds at Shelby over the Coosa. The 
great bulk of the brown ores of Alabama is from this 
horizon. 
At the top of the Knox Dolomite, and belonging perhaps 
tothe next succeeding division, there is a rather peculiar 
rock occurring at intervals along Jones’ Valley and else- 
where. Itis a breccia made up of angular fragments, chiefly 
of the chert of the Knox Dolomite, cemented together into 
a rock which is a good many feet in thickness. This rock, 
being made of fragments of the Knox Dolomite, is of course 
younger, though on account of its materials we have usually 
classed it along with the Knox Dolomite. It is seen in 
greatest volume in the Salem Hills southwest of Bessemer, 
but occurs upon the Flint ridge forming the North High- 
lands at many pionts, e. g. Birmingham and Gate City, and 
also west of Springville. It has been called the Birming- 
ham breccia by Mr. Russell of the United States Survey, 
and Salem breccia by us in the State Survey. It is of in- 
terest as showing that a period of disturbance intervened 
between the time of the formation of the Knox Dolomite 
and that of the Trenton Limestone. We have not attempted 
to show on the map the occurrences of this rock, 
Trenton or Pelham Limestone.—As its name implies, this 
division is mostly calcareous. It may be perhaps as a 
maximum, 800 feet or more in thickness, and varies con- 
siderably in quality, the lower part being ususally impure 
and shaly, while the upper part is mostly a pure limestone, 
often used for the purpose of making lime and as a flux in 
the furnaces. The lower part commonly holds great number 
of shells of Maclurea magna, which is a characteristic fossil 
of the Chazy limestone of the New York Geologists. The 
purer limestone above, is also quite full of fossils, which, as 
