AND COAL-MEASURES OF IOWA. 105 
to return after making the astronomical observations necessary to determine our 
position, which was found to be in latitude 42° 39’ 06”. 
The preceding sketch conveys a very correct idea of the appearance of this desolate 
region of drift knolls, as seen from one of their summits, with the wilderness of 
prairie stretching away to the northwest. 
There remains to be said, in this place, only a few words with regard to the 
extreme western branches of Red Cedar, viz., Beaver and Otter Creeks, which were 
explored by Mr. Macy, with a view to ascertain the Bryne eastern boundary of the 
carboniferous rocks on the Iowa River. 
On account of the low, wet country bordering these streams, it was only at a few 
points that the rocks were visible, and these only in low ledges, near the water-level, 
or in partial protrusions from under the mass of drift in the higher ground. 
Mr. Macy succeeded, however, in detecting, in a ridge about five miles north of 
Otter Creek, a flesh-coloured limestone, containing that variety of Leptena depressa 
of Dalman, which occurs in the Corniferous Limestone of New York, and is known 
there under the name of Strophomena undulatus. At a higher level in the same 
ridge a buff-coloured magnesian limestone was observed, in which no fossils were 
discovered, but which possesses the lithological character of the dolomitic beds of 
the carboniferous limestones found near the Iowa, a few miles below the Rapids, 
near latitude 42° 30’. Thus, the dividing ridge between the head waters of the 
extreme western branches of the Red Cedar River (Otter Creek and Elk Fork), is 
probably the boundary between the limestones of the Devonian and Carboniferous 
Eras. 
In consequence of a severe intermittent which Mr. Macy contracted while travers- 
ing the low fens of this section of Iowa, exposed to the intense heat of a July sun, 
he was prevented from prosecuting his investigations further north. 
Carboniferous Rocks of the Des Moines, below the Raccoon Fork.—The first good 
section exposed on the Des Moines is at St. Francisville. The Archimedes lime- 
stone occurs here, a few feet above low-water mark; and upon it rest several 
members of the Carboniferous Limestone, in the order represented on Section 
No.4, D.* 
The geodiferous beds which immediately overlie the Archimedes limestone, are 
here mostly concealed by the alluvion of ghe Des Moines, and the talus from the 
superior strata. The St. Francisville quarry affords, however, a good opportunity 
of examining the buff-coloured rock, which lies about fifty feet above the bed of the 
Des Moines, with a face of about ten feet exposed. It is at present obtained here, 
for the construction of the public works in the vicinity, in large blocks, from two to 
three feet thick. This rock is of a decided dolomitic character, yielding by analysis 
thirty-seven per cent. of carbonate of magnesia, and fifty-six per cent. of carbonate 
of lime. Its specific gravity is considerably below the average of common lime- 
stones, being but 2°589; a property which must be considered an advantage, 
regarding it as a building material. Its durability has not been fully tested; but — 
* The Sections in this chapter designated as No. 1, D, No. 2, D, &c., are the Sections on the Des Moines 
River. 
14 
