Sioux City Academy of Science and Letters. 147 
Lying unconformably over the eroded surface of 
these sediments are unconsolidated Quaternary materials 
consisting of a heavy covering of loess with thin and 
scattered deposits of glacial till and sands as its base. 
No igneous or metamorphic rocks outcrop in Dakota 
County and no sedimentary beds of pre-Cretaceous age. 
The well at Sioux City, Iowa, 2,011 feet deep, probably 
reached the base of the Cretaceous sandstones at 540 
feet, and, passing through Paleozoic limestones, shales, 
and sands to a depth of 1,510 feet encountered a pre-Pal- 
eozoic rock 15 feet thick that resembled the Sioux quartz- 
ite, below which it entered a micaceous schist. The 
quartzite has been referred to the Algonkian system, 
while the schist is regarded as Archean. ®The well at 
Ponca, Nebraska, 698 feet deep, entered at 455 feet lime- 
stone, which is probably pre-Cretaceous, and may belong 
to the Pennslyvanian series of the Carboniferous system.” 
These records indicate that Cretaceous strata continue 
to a depth of between 250 and 350 feet below the present 
bottom of Missouri River, and that the surface on which 
the Cretaceous strata rests is very uneven. 
DESCRIPTION OF FORMATIONS. 
Dakota.—The lowest beds of this formation exposed 
within the county appear at the Homer quarry and along 
the bluffs to the southeast. The top of the formation is 
about 80 feet above Missouri River at the south line and 
about 20 feet above at the north line of the county. Just 
south of Jackson a slight anticline carries the beds down 
to about the same level as they occupy at the north 
county line. 
The following sections have been observed: 
SECTION OF DAKOTA SANDSTONE ABOUT 4 MILES 
SOUTHEAST OF HOMER. 
Thickness 
Feet. 
MOCSSVETASSEAVOVED SIOPS Ae owae Ge ie Sie ee ales alae aljeleyalslens, elds 
2. Sandstone and clay, thin bedded, iron stained................ 16 
1. Sandstone, massive, cross-bedded, from loose and friable to 
quartzitice. Colors Meht) toy GUStYyeereie alae cioslse eles a cinieans 20 
aBain, H. F., Geology of Woodbury County: Iowa Geol. Survey, 
Vol. 5, 1895, pp. 265-273. 
bDarton, N. H., Geology and underground water resources of the 
Central Great Plains: Prof. Paper, U. 8. Geol. Survey, No. , 1904, 
(in preparation). 
