66 PROTOZOIC ROCKS 
mingle in the distant horizon. The whole combination suggests the idea, not of an 
aboriginal wilderness, inhabited by savage tribes, but of a country lately under a 
high state of cultivation, and suddenly deserted by its inhabitants,—their dwellings, 
indeed, gone, but the castle-homes of their chieftains only partially destroyed, and 
showing, in ruins, on the rocky summits around. This latter feature especially 
aids the delusion ; for the peculiar aspect of the exposed limestone, and its manner 
of weathering, cause it to assume a resemblance, somewhat fantastic indeed, but 
yet wonderfully close and faithful, to the dilapidated wall, with its crowning 
parapet, and its projecting buttresses, and its flanking towers, and even the lesser 
details that mark the fortress of the olden time. The wood-cuts towards the 
beginning and at the end of this section, as well as the one here inserted, repre- 
sent actual exposures of the Lower Magnesian Limestone on the Upper Iowa. 
They will convey a better idea than any written description of the nature of the 
scenery on that picturesque river. 
ea TN 
ii WZ Uiipet / 
LOWER MAGNESIAN LIMESTONE, UPPER IOWA. 
Bold exposures of rock, with a grassy bank beneath, such as here depicted, are, 
for the most part, only on the south and western sides of the hills; the northern 
and eastern declivities are more rounded, and, most generally, overgrown with trees 
and shrubbery, as illustrated by another scene on the same stream introduced on the 
opposite page. It seems as if the alternate thawing and freezing on the sunny side 
has caused a more rapid decay of the rock, which scaling and splitting off, sometimes 
in large masses, slips down the side of the hill; this, together with the rapid transition 
from heat to cold on the southern exposure, probably prevents trees from coming to 
maturity on that side; or, it may in part be due to some more general law, that has 
regulated the elevation of these Magnesian Limestones in determinate lines ; thrust- 
ing the beds up to the north of the line, while a depression occurred on the south. 
In some instances the hills seem as if split down the middle, one side being left 
standing whilst the other had been entirely carried away. La Grange Mountain, 
at the head of Lake Pepin, introduced on page 46, and the Cap de Killio, below 
the Wabasha Prairie, may be cited as examples in point. 
There is a striking analogy between the physical features of the country occupied 
