ON THE WISCONSIN RIVER. 519 
extending down to the water. The soil above is light and sandy ; the growth, only 
small pines and scrubby oak. 
Beyond this exposure, the alluvial banks of the river are about ten feet high. 
From these bottoms there rises a gradual slope to a terrace of land fifty feet above 
the Wisconsin. 
With the exception of some low ledges of rock, about four miles above this last 
section, there are no exposures for thirteen miles. Cliffs of variegated sandstone 
of F'. 1 then again present themselves, with mural faces of about twenty feet, over 
which are two terraces of land, one about forty-five or fifty feet above the river, 
the other still higher, and consisting chiefly of sand. The rocks are still more 
singularly worn and weathered, so as frequently to produce the effect of a ruined 
temple, half sunk in the water. Two miles beyond this, a terrace of sand, with a 
few thin layers of ash-coloured clay, commences on the west side of the river, and 
rises to the height of twenty feet, continuing for three miles. 
From this terrace Petenwell Peak can be seen, two miles off, looming up out of 
these sandy plains. It is the most elevated of all the isolated peaks measured on 
this part of the Wisconsin, being two hundred and fifty-five feet above the 
river. Its east face is nearly perpendicular; on the west is a very steep slope, 
one hundred and sixty feet above the surface of the plain, thickly strewn with 
immense blocks of sandstone. The north side is worn into several subordinate 
peaks, but little inferior in height to the main mass, being about two hundred 
feet above a creek which flows near their base. 
The rocks near the summit of Petenwell Peak consist of coarse and fine-grained 
white, yellow, and ash-coloured sandstone, in thick beds, with some thin layers 
interstratified. The area of ground on the summit of the highest peak is only 
about twenty-four hundred square feet, its length being about two hundred feet, 
and its average width about twelve. The base of the exposure of rock is a mottled, 
ferruginous sandstone, with occasional concentric markings. 
It is a matter of surprise to the spectator of this vast pile of sandstone—which is 
mostly soft, crumbling even with a slight blow of the hammer—how it should have 
resisted the denuding action which has swept away hundreds of feet of similar 
sandstone from around it. The explanation of the phenomena may perhaps be 
found in the fact that some of the beds seem to have a disposition to indurate by 
exposure, acquiring in time a hardened, vitreous surface, approaching to quartzite, 
which gradually incrusts the softer material within. We must suppose, therefore, 
that for a time the locality of the Peak was protected from the more rapid current 
which carried away the adjacent rocks, until gradually having acquired a more 
indurated face, it was enabled to withstand agencies which, in its original condi- 
tion, must have inevitably ground it to sand, as they have done the adjacent 
strata. 
The summit of Petenwell Peak affords an extensive prospect of the surrounding 
country. At its foot is spread out a gently undulating grassy plain, dotted with 
groves of oak and pine, with here and there a huge isolated peak, towering up like 
some artificial monument, commemorating the long lapse of time during which 
powerful currents must have circulated around them, gradually carrying away and 
