A LARGE COLONY OF FOSSIL CORAL * 
A. O. THOMAS. 
The abundant coralline remains preserved in the Niagaran 
beds in sections five, six, and seven, Scotch Grove township, Jones 
county, have been strikingly pointed out by Calvin in his 
Geology of Jones County . 1 In this locality the corals formed a 
magnificent reef and with few exceptions they are now preserved 
completely silicified and are imbedded in a soft dolomitic matrix 
which upon weathering leaves the corals among the residual 
products. The few corals that have not been replaced by silica 
occur in the form of highly crystalline limestone which upon 
being sectioned and polished shows the internal character of the 
corals fairly well. In a few cases tubular cavities in the dolomite 
represent the former presence of stems of colonies of Diphyphyl- 
lum, Syringopora, or others. 
Considerable weathering with resultant concentration of the 
silicified corals in the thin soil had evidently preceded the in- 
vasion of the region by the Pleistocene glaciers ; consequently, the 
geest, now either exposed or buried by a mantle of thin drift, the 
aggraded valleys, and in some cases the drift itself contain locally 
an abundance of well preserved corals. Post-Pleistocene erosion, 
especially the re-excavation of some of the eld valleys has laid 
bare thousands of specimens and many ravines are strewn with 
them for hundreds of yards. The thin-soiled hills of the region 
are likewise thickly dotted with large and small coralla. 
Near the head of a small gully developed in recent years the 
following section shows the succession of strata in its sides : 
Feet 
4. Black sandy loam with chips of chert and occa- 
sional foreign pebbles of glacial origin. 2-4 
3. A coral bed made up of long cylindrical stems, 
subparallel and closely aggregated. In the upper 
three to six inches the stems are broken into 
short pieces and are imbedded in a brownish, 
sticky geest; in the lower part the stems are 
less broken and are imbedded in a soft, buff- 
colored dolomite . 1-1% 
*Published by permission of the Director of the Iowa Geological Survey. 
Uowa Geol. Surv., Vol. V., pp. 79-81, 1896. 
