144 Geology of Upper Illinois. 
Rockwell is situated on section fourteen, which is next to the 
section against which the canal terminates. The width of the 
Illinois valley varies in this vicinity from one to two miles. Its 
bluffs, which are generally of naked rock, and nearly perpendicu- 
lar, are between one hundred and one hundred and twenty feet in 
height. Their course and position with respect to the channel of 
the river, may be seen upon the accompanying map. ‘The bot- 
tom of the river in the vicinity of Utica is solid rock, with which 
also the bottom-lands are underlaid at very partial depths. 
deed, the strata often attain the surface over considerable breadths 
of the meadows between Rockwell and Ottawa. The course of 
the canal, which is also traced on the map, is directly at the foot 
of the northern bluff. 
sian limestone in Wisconsin, Upper Illinois, and Missouri, struck me with sur- 
gan, the islands about Michillimacinac, the mouth of Green bay, as well as near 
pm ee at the head of the bay. In the last mentioned region, it abounded in a 
Producta, which I take to be undescribed, and shall therefore denomi- 
nate a incure. ific character. Semi-circular: hinge nearly straight and 
the — = ee ans with Sane _giiaene = strie ; flattish ; edge crenated ; shal- 
res valve ine ; muscular impressions and hinge-pro- 
very neg a3 ira 3 2.) "The ae between the valves is very small 
in “es species. 
Fig. 3, represents a second species of the 
same genus, which is also grea new. The 
large walee e is deep an ry gibbous. Its strie 
are distinct, and eabebia the ‘ibe of the Pee- 
tens. 
Along with these species occurs a polypifera, 
apparently belonging to the genus Flustra. 
