486 CLARK AND BIBBINS 
to hydrous oxides of iron, which the miners recognize under 
or ‘‘red”’ ore. Under these conditions 
d 
the name of ‘‘brown’ 
also the originally drab-colored clays containing the carbonate 
Fic. 2. Section at Reynold’s Mine, Anne Arundel County, showing Arundel 
clays overlain by Patapsco formation. 
ores have suffered a like chemical change, resulting in red or 
variegated clays. Where these clays chance to contain but 
little lignite the iron ore may consist almost entirely of these 
oxides. 
The peculiar relations which the Arundel formation presents 
to the other members of the Potomac group render it difficult to 
say much regarding the strike and dip of the deposits, although 
the fact that they lie exposed in depressions upon the surface of 
the Patuxent formation renders it probable that these’ features do 
not differ materially from that observed in the other formations. 
The lenses vary greatly in thickness, and from their charac- 
ter are at times lacking in portions of the country. The esti- 
