CARBONIFEROUS LIMESTONES OF IOWA. 95 
place in the zoological systems, and fill up gaps in the existing orders of the animal 
and vegetable kingdoms. 
To think that we, at this day, can demonstrate the structure of the eye of some 
of these—the most ancient races—and even count the thousand lenses by which 
light was concentrated to the optic nerve, is truly astonishing! Is it then sur- 
prising that it should engage the most earnest attention of the closet philosopher, 
and awaken the enthusiasm of the enterprising explorer? 
But paleontology is not a study of mere curious, scientific inquiry; it has, also, 
its practical inferences, and these of the most important character, with their 
direct, matter-of-fact bearings. In illustration of this view of the subject, permit 
me, in this connexion, to direct the attention of the reader to Figs. 1, 5, and 6, of 
Table IV. The fossil corals represented by these engravings are found embedded in 
the subcarboniferous limestones, and near the top of the series; always under the 
true coal-bearing beds; never above these, or included in them; and nowhere else. 
This geological fact holds good not only in Iowa, but throughout the entire range 
of the subcarboniferous limestones in Indiana, Illinois, Kentucky, and Tennessee. 
In not a single instance, from the range of the Cumberland Mountains on the east 
to the interior of Iowa on the west, has a workable bed of coal been discovered in 
a position beneath the strata of limestone containing these corals. In these organic 
remains, then, we find the surest, the most unerring guide in the search after this 
invaluable article of commerce, that warms our houses, that drives our steam- 
engines, by which we navigate our rivers, lakes, and oceans; that propels the 
machinery, by which we weave our fabrics; that reduces our iron, by which we 
cultivate our soil, and carry on every conceivable mechanical operation; that 
refines our metals, that contributes to the production of both the necessaries and 
luxuries of life, and by which we transmit intelligence, with the swiftness of light- 
ning, to stations the most remote. Without the knowledge of this fact, millions of 
dollars might be expended—have been expended—in fruitless and hopeless mining 
operations after geological incompatibilities. 
All the figures on Table V., A and B, are equally persistent in their unde- 
viating geological position, quite below the productive coal-measures, as well as 
beneath these same coral-bearing beds. 
In stratigraphical paleontology we have, then, the safest and the most trustworthy 
index to direct our explorations after mineral treasures in the fossiliferous strata. 
Taken as a whole, these carboniferous limestones are rich in organic relics. The 
lowest fossiliferous bands, under the odlitic bed, are particularly characterized by 
remains of bivalve Mollusca, belonging principally to the genera Chonetes, Spirifer, 
Posidonomya, Archa, and Allorisma. Tn consequence of these being chiefly casts, it 
is rarely possible satisfactorily to determine the species. Associated with these is 
occasionally found a Phillipsia. 
The oblitic bed contains Productus cora, Spirifer striatus, and a gigantic species 
of Gyroceras, to which (from the locality where found) the name Burlingtonensis, 
has been given.* 
* See Table V., Fig. 10. 
