12 The AmericADl (Teoloijisl. January, isy.i 
the Florence sand. The geographic distribution of the Val- 
ley loess is nearly cr)extensive with that portion of the district 
which lies lower than a plane 100 feet above the river level at 
Freeport. In ascending the Pecatonica river, the deposit is 
first met with on the north ^side of the valle}^ near the month 
of Sugar river. Here it forms a nearly level though discon- 
tinuous terrace, 50 feet above the river, and runs west along 
the foot of the bluffs to the Stephenson' county line, bej'ond 
which it is less distinct, though occuring at intervals on both 
sides of the valley. At Freeport its hight has decreased to 30 
feet, and northwest from there it rarely forms any prominent 
terrace. Wells drilled into this terrace usually penetrate 
about 20 feet of fine silty loess, and then 80 feet of brown 
stratified sand. This brown sand, or lower division of the 
Valley loess, is raoderatel^^ coarse-grained at the base, where 
it often contains small pebbles and much ferruginous matter. 
The material gradually grows finer from the base upward, and 
from east to west in the valley. At the same time the strati- 
fication and lamination become less distinct as the material 
grows finer, and there is less evidence of wave and current ac- 
tion. The thickness of the deposit is something over 30 feet 
in the lower portion of the Pecatonica valley and decreases 
westward. It occurs only at the lower levels of the deeper 
valleys. In the vicinity of Freeport, and eastward down the 
valley, it has its greatest thickness below the level of 25 feet 
above the flood-plain of the river. Above this it thins out in 
passing up the sides of the vallej-, and it has not been recog- 
nized at hights more than 60 feet above the flood-plain level. 
Throughout the Pecatonica valley from the mouth of Sugar 
river to Winslow, near the state line, this division of the loess 
maintains a nearly uniform constitution, being everywhere an 
easily recognized bed of brown sand. But in passing up the 
valley of Yellow creek we find a change, sand deposits belong- 
ing to the loess occurring only in scattered patches. Instead, 
we find a few feet of highly ferruginous, indistinctly lami- 
nated clay, underlying the easily recognized upper division of 
the Valley loess. The iron oxide was probably derived from 
the old soil on the ridges near b}^, and in some places it is 
present in such amount as to give the deposit the appearance 
of an earth}' iron ore. 
