ROCK FORMATIONS OF THE WESTERN STATES. 511 
limestone is wanting, its fossils appearing only in a few places in shale and sandstones asso¬ 
ciated with the coal strata. 
For the greater part of the distance along which this limestone was seen, it is but slightly 
inclined, often appearing horizontal. The only deviation of importance noticed, is near Her¬ 
culaneum, on the Mississippi river. At this place there appears to have been an extensive 
uplift in a northeast and southwest direction, elevating the strata at an angle of thirty degrees ; 
and from the existence of one or two small islands, seems, at some remote period, to have 
obstructed the course of the river. From the shallow water at this place, the uplift appears 
to have been of more recent origin than the excavation of the river channel, otherwise there 
appears no reason why the depth here should not be as great as in other places. 
Along the Mississippi river the common fossils are a large species of Delthyris, with a 
smooth Orthis or Atrypa, in form like the A. concentrica of the lower rocks, but larger ; these 
appear at numerous localities which I had opportunities of examining. Several species of 
Productus, with the larger valve very much arched, and the upper one concave and slightly 
wrinkled, are constant, and good guides for this mass. My friend Dr. Owen has figured some 
of the common forms in the American Journal of Science.* Residing upon this formation, 
his opportunities of investigation are ample, and we may expect that his zeal will lead to the 
full development of its interesting organic contents. 
After leaving the carboniferous limestone, near the mouth of Rock river, the coal and as¬ 
sociated rocks appear, and beyond this point the lower limestones ; the intermediate rocks 
not being seen. There is evidently either an abrupt synclinal axis, or fault, which has brought 
up the lower masses. From want of sufficient time to investigate this point, I was unable to 
determine the precise cause, or amount of change. The contrast between the two limestones 
thus brought into proximity, is very striking ; the grey or ashen color is exchanged fora brown 
or iron-stained rock, harsh to the touch, and composed of small crystalline grains. The mass 
rises in broken or detached knobs or pinnacles, presenting a ragged and irregular outline, in 
place of the uniform cliff formed by the higher limestone. In tracing this limestone up the 
river as far as Galena, its lithological character is the same as that of the middle and upper 
portions of the Niagara limestone, and all its associations are the same. The cliffs in many 
places, particularly on the river above Dubuque, have all the appearance of those at the Falls 
of Niagara, so far as regards lithological character, weathering, etc. Above the town of Du¬ 
buque, this rock (cliff limestone) rests upon the blue limestone, which, according to Dr. 
Owen’s statement, is much thinner here than in Ohio ; but not having traced it to its termina¬ 
tion below, I am unable to speak from personal observation. Specimens which I saw from 
the lower part of this rock about Praire du Chien, indicate the presence of the Trenton and 
Black river limestones, by the large Orthocerata and other fossils. From a section made by 
Dr. Owen, it appears that there are beds of sandstone, interstratified with, and underlying 
the blue limestone. 
Vol. xliii, page 14. 
