FOURTH ANNUAL YEAR BOOK — PART II. 125 



level. The driftless area is a land of thin soils, high, rocky precipices, long 

 steep hills and deep rock-cut valleys. It is a picturesque land. The main 

 streams have made valleys that are from 600 to 700 feet in depth, measured 

 from the higher points to the divides. The upper Iowa— or the Oneota as it 

 might better be called— flows between rockv bluffs which in places rise almost 

 sheer to a height of 300 feet above the level of the water, and from 

 their summits the surface, in many long swells and undulations, rise 300 

 feet higher to the tops of the dividing ridges which are back some miles 

 from the stream. The whole surface of the driftless area has been carved 

 into an elaborate system of branching and re-branching trenches separated 

 by steep-sided ridges. The details of topography resulting from erosion are 

 governed to no small extent by the geological structure of the region. The 

 picturesque escarpments, buttresses, towers and castles which crown the 

 bluffs and give charm to the scenery along the lower courses of the upper 

 Iowa are due to the effects of the weathering on the hard, resistant, dolomitic 

 formation called the Oneota limestone. We owe the impressive scenery above 

 and below Decorah, culminating in those majestic cliffs at Bluffton, to the 

 presence and characteristics of the Trenton limestone. The Galena lime- 

 stone gives us the splendid castles, towers and other grand scenic effects 

 about Dubuque. For the great Niagara escarpment, probably one of the 

 most striking of the topographic features of the driftless area, we are indebted 

 to another hard dolomite, the Niagara limestone. The Nia2:ara escarpment 

 forms the steep acclivity, looking like a line of bold hills, which curves 

 around Dubuque at a distance of six or seven miles to the west and culmi- 

 nates toward the southwest in the high, promontory-like salient known as 

 Table Mound. The escarpment makes up those conspicuous cliffs seen 

 crowning the long slopes which form the walls of the valley of the little 

 Maquoketa in the vicinity of Graf. It zigzags back and forth to accommo- 

 date itself to the rims of numerous small valleys opening to the Mississippi, 

 between Table Mound and Bellevue. North of Dubuque the escarpment 

 forming Niagara expresses itself in the steep slopes of Sherrill's Mound, and 

 in a number of other prominent and symmetrical buttes of circumdenuda- 

 tion; and across the river, over yonder in Wisconsin, the eastern sky line is 

 broken by another mass of Niagara, the far famed Sinsinewa. 



The Maquoketa shales are the most important of the slope making 

 formations coming to the surface in the driftless area. The gently inclined 

 and largely cultivated plain, more or less trenched by erosioQ, which lies 

 between the summit of the precipitous bluffs of Galena limestone at 

 Dubuque and the foot of the steep Niagara escarpment six or seven miles to 

 the west, is due to the presence of the Maquoketa shales. At some points 

 near Graf the slope due to the Maquoketa is less than a mile in width, and 

 detached blocks of Niagara limestone, loosened by frosts and other agen- 

 cies from the escarpment above, gradually creep down the inclined surface 

 to be at last precipitated into the stream over a cliff of Galena limestone. 

 At no points are there better illustrations of the effects of structure on 

 topography. Here are two hard limestones separated by shale; two steep 

 escarpments separated by cultivated slopes. 



Had it not been for the incursion of glaciers and the distribution of drift, 

 the whole face of Iowa would have resembled the driftless area in many 

 particulars. Thin soils, bare rocks, steep precipices and deep valleys would 



