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 Pe ten well 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 



