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. 



lOWEIi 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 



