Geological Surface Features of Sauk County. 511 
glomerate. Farther away from the Archaean the sandstone is 
capped by Lower Magnesian limestone, which in the depression 
occupied by parts of the townships of Prairie du Sac and Troy 
reaches a thickness of about one hundred feet. 
The town Prairie du Sac, situated in the southeastern part of 
the county and bordering on the Wisconsin river, exhibits the 
same general southeast slope as that part of the county. At the 
northeast corner of the town we find the surface of the river 
one hundred and seventy-two feet above Lake Michigan. At 
the Sauk City bridge a height of one hundred and sixty-eight 
feet, and at the southwest corner of the town about one hundred 
and sixty feet. 
Notwithstanding that the term “Sauk Prairie” is frequently ap¬ 
plied to the surface of the town, a detailed analysis shows, that, 
instead of being an undulating prairie, it is composed of a 
series of terraces rising from the river to the northwest. By 
a.scending these terraces we are enabled to note the vegetation 
of each. The river itself and its two tributaries, Otter and Honey 
creeks, do not, on account of the rapid flow necessitated by 
the decided slope of the country, furnish us with an exten¬ 
sive aquatic vegetation. Only some pools show an abundance 
of Elodea Canadensis, Potamogeton amplifolius, P. spirillus, 
P. Eobbinsii (?) and Spirodela polyrrhiza, with occasional colonies 
of Nuphar advena and Nymphaea tuberosa. 
Commencing our survey at the river bank in section 14, town 
9, range 6, we find the river bank built up to a height of about 
six feet by pinkish and yellowish sand, disposed in thin layers, 
and with the frequency of false bedding peculiar to stream-built 
strata. Above the sand we find a variable thickness of vege¬ 
table mold reaching in some places three feet in thickness and 
in some places grading into peat of varying degrees of decompo¬ 
sition. 
Having ascended this almost barren bank we stand upon a 
nearly level tract of land extending northward about one mile 
and following the river for a distance of about three miles. The 
subsoil is a heavy bluish clay, upon which follows a bed of fine 
white sand, which is again succeeded by vegetable mold. This 
on account of the level surface and imperviousness of subsoil is 
