Fire-Clay Pockets at Clinton, la. — Farnsworth. 331 
POCKETS CONTAINING FIRE-CLAY AND CARBONACEOUS 
MATERIALS IN THE NIAGARA LIMESTONE AT CLIN- 
TON, IOWA. 
By P. J. Farnswokth. 
In the first volume of the geological reports of Iowa, 1854, 
an account is given of certain caves or openings in strata of 
the age of the Niagara and Devonian limestones filled with 
what is supposed to be the under-clay of the coal formation. 
One described and figured is in the quarry near Rock Island. 
Such cavities are numerous in the lower part of the Niagara, 
about Clinton, and are also mentioned as occurring in the 
Galena in the lead mining country about Dubuque and Galena. 
There is also one figured and described in the Devonian near 
Iowa City. 
The one described in the quarr}'^ at Rock Island answers to 
several that I have examined in the vicinity of Clinton. " The 
surface of the rock beneath the superincumbent soil presents 
a depression which deepens into a broad funnel-shaped cavity, 
gradually narrowing below till within ten feet of the bottom, 
when it spreads out on one side with an irregularly arching 
roof and an unequal floor. It is filled from top to bottom with 
hard clay, similar to the under-clay of the coal seams. * * 
The laminations of this clay conform to the curvatures and 
irregularities of the roof and floor of the ancient cavern and 
exhibit the appearance of having flowed in while in a semi-fluid 
condition, while the hydrostatic pressure of the mass above, 
acting through the deep funnel had forced the soft mass 
against the walls and roof of the cavity, causing it to assume 
in its lamination the same contour." 
" [n the midst of this clay was the impression of a large 
Euomphalus very similar to a carboniferous form, * * with 
this exception, no fossils were observed in the clay of this 
locality." 
''In a section near Iowa City in a cliff of limestone of the 
Hamilton group between beds of a nearly horizontal limestone, 
appears a black band extending thirty or forty feet; this 
consists of black carbonaceous mud, the upper part having the 
character of cannel coal, and the lower part a slaty carbon- 
aceous shale. Beneath this and less extended a thicker layer of 
