288 
GEOLOGY OF THE FOURTH DISTRICT, 
The illustration above exhibits these seams as they appear in two blocks of conglomerate at 
Rock city. The seams are an inch thick ; the lower one at the left hand folding irregularly 
around, and enclosing a portion of sand : the same concretionary tendency is seen in a part 
of the seam on the right hand side. 
The illustration No. 136 represents a thicker seam of the ore upon the surface of a loose 
block, where the weather has removed the rock above. This shows a tendency to folding, 
as in the other instances. Small nodules are sometimes found, though rarely, which do not 
enclose sand. 
136. 
The existence of these seams, and the concretionary structure is noticed here, from the fact 
that farther westward, small concretions of ore, and concentric seams similar to these, are of 
frequent occurrence, and seem to characterize the mass. 
At the Cuyahoga falls in Ohio, the cliff of conglomerate presents some interesting exhibi¬ 
tions of these seams, which the following woodcut illustrates :* 
137. 
Fig. 1 is an example where two centres are formed, which are subsequently enveloped by concretionary laminae. 
Fig. 2 exhibits concentric rings or laminae, which expand farther upon one side. 
Fig. 3 presents irregular concretionary or concentric laminae, enclosing a few undulating ones, but with no well defined centre. 
* See Transactions of the Association of American Geologists and Naturalists, Vol. 1. 1813. 
