These particular forms have resulted from the peculiar weathering of the quartzite. The rock is affected by several systems of vertical or nearly vertical joint planes (cracks), which divide the whole formation into a series of vertical columns. There are also horizontal and oblique planes of cleavage dividing the columns, so that the great quartzite pile may be said to be made up of a series of blocks, which are generally in contact with one another. The isolated pillars and columns which have received special names have been left as they now stand by the falling away of the blocks which once surrounded them. They themselves must soon follow. The great talus slopes at the base of the bluffs, such as those on the west side of the lake and on the East bluff near its southeast corner, Plate XXIV, are silent witnesses of the extent to which this process has already gone. The blocks of rock of which they are composed have been loosened by freezing water, by the roots of trees, and by expansion and contraction due to changing temperature, and have fallen from their former positions to those they now occupy. Their descent, effected by gravity directly, is, it will be noted, the first step in their journey to the sea, the final resting place of all products of land degradation. _The Baraboo bluffs._--Nowhere in southern Wisconsin, or indeed in a large area adjacent to it, are there elevations which so nearly approach mountains as the ranges of quartzite in the vicinity of Baraboo and Devil's lake. So much has already been said of their history that there is need for little further description. Plate IV gives some idea of the appearance of the ranges. The history of the ranges, already outlined, involves the following stages: (1) The deposition of the sands in Huronian time; (2) the change of the sand to sandstone and the sandstone to quartzite; (3) the uplift and deformation of the beds; (4) igneous intrusions, faulting, crushing, and shoaring, with the development of schists accompanying the deformation; (5) a prolonged period of erosion during which the folds of quartzite were largely worn away, though considerable ridges, the Huronian mountains of early Cambrian times, still remained high above their surroundings; (6) the submergence of the region, finally involving even the crests of the ridges of quartzite; (7) a protracted period of deposition during which the Potsdam sandstone and several later Paleozoic formations were laid down about, and finally over, the quartzite, burying the mountainous ridges; (8) the elevation of the Paleozoic sea-bottom, converting it into land; (9) a long period of erosion, during which the upper Paleozoic beds were removed, and the quartzite re-discovered. Being much harder than the Paleozoic rocks, the quartzite ridges again came to stand out as prominent ridges, as the surrounding beds of relatively slight resistance were worn away. They are "resurrected" mountains, though not with the full height which they