Correspondence. 263 
l)ed is somewhat darker than that at Muscatine. At Rock Island, Illi- 
nois, the same bed has been encountered in several wells. In one of 
these, near the crossing of Thirty-fifth street and Seventh avenue, the 
materials penetrated consisted of loess, apparently two sheets of till, silt 
varying from a black to a grayish loess, with small gasteropods, and 
then a greenish, sticky clay containing fragments of the bed rock, but 
apparently no Archean pebbles or bowlders. This latter clay was five 
feet in thickness and rested on shales and clays of the Coal Measures. 
It seemed to be residual material of preglacial age. The silt and muck 
above it contained fragments of wood, one of which measured nearly 
two feet in length. Silt of the same and in the same position, but oxi- 
dized and without fragments of wood, has been expo.sed in grading some 
of the streets near by. On Thirty-ninth street it contained the follow- 
ing fossils: Helicina occulta Say, Pupa alticola IngersoU, Pyraniidula 
sfriatella Anthony and Siiccinea aimra Say. Similar deposits, without 
fossils, occur under the drift in the bluf¥s east of Cordova, Illinois, and 
in the northern part of Clinton, 'Iowa. At the latter place they are 
finely lam.inated and are associated with a peaty or soil-like layer. A 
deposit which appears identical with the loess-like silt on Thirty-fifth 
street. Rock Island, is fo^und underlying till on the east line of section 
12, T. 17 N., R. I W., south of the city, and another occurs in the bluiTs 
of the Mississippi river in the west end of the county. At the first of 
these localities the deposit rests on Coal Measures and contains the fos- 
sils already mentioned as occurring at Thirty-ninth street. At the ex- 
V'Osure in the west end of the county the underlying beds are not seen. 
The total thickness of the overlying drift is about 100 feet. Shells are 
abundant, and according to the determinations of Dr. W. H. Dall they 
include Helicina occulta Say, Helicodiscus lineatusSay, Litnncea hiu/n'/is 
Sa.y, Pupa armifera Say, Pyraniidulaperspectiva Say, Pyramidula striat- 
rlla Anthony, Strobilops lahyrinthiea Say, Succinca avara Sa\ , Succinra 
hiteola Say, Polygyra, sp,. Vitrwa arborea Say. 
These loess-like deposits have a bluish green color in fresh expos- 
ures, but one season of weathering gives them a reddish gray hue to 
the depth of one (n* two feet, and then their resemblance to the loess in 
color as well as in structure is quite marked. Even the tubular, fer- 
ruginous concretions of the latter deposit appear. 
The precise relation of the soil beds to this deposit and to the lamin- 
ated silts with which it seems to be associated, and the relation that 
the two latter have to each other, can, not be fully made out from the 
known exposures. In the well on Thirty-fifth street there seemed in- 
deed to be two soil horizons. The section under the Kansan till was as 
follows, beginning above: 
1. Black sticky muck with lar^'c fratfinonts of wood 4 feet. 
2. Loe.s.s-likis ash colorfd niaterial. with pulmonato fossils. K " 
X Black Muck 4 " 
4. Residual clay full (if local rock fraunients 5 '" 
5. Coal Measures (Exposed.) 
