366 
The American Geologist . 
June, 1896 
the drift covered area.* Although thus well within the terri¬ 
tory whose surface has been moulded by ice action, the bluffs 
of the South Maquoketa show at some lower levels the general 
characters of the Driftless Area. With regard to the lower 
portion of the Maquoketa river, McGee says :f “ In the valleys 
east of Deep creek, little if any erratic material occurs among 
the superficial deposits. At the same time the summits and 
divides are rounded and stretch off to the eastward in grace¬ 
fully curved dolphin backs, such as everywhere tell of ice 
action: and the testimony of form is corroborated by that of 
material, for occasional bowlders peep out from the upper 
slopes, and patches of gravel are turned up by the plow and 
exposed in the roadside gullies over the uplands. 
“ This hybrid configuration is one of the most striking 
phenomena of northeastern Iowa. It seems anomalous, incon- 
grous, almost incredible, that the hill tops Should be moulded 
into the long and gracefully rounded swells of rock turned 
out from the ice mill, and that in the same vicinity the older 
valley bottoms should exhibit the rugose aspect of water 
sculpture; but the fact is patent to any observer and indeed 
forms the conspicuous topographic feature of the drift border 
region.” 
What is here stated for the regions near the mouth of the 
stream is true in numerous places of its valley walls as traced 
through Jones and Delaware counties. Erosion towers, cas¬ 
tellated turrets and balanced rocks, which are among the 
strongest evidences of the absence of ice action in the. Drift- 
less Area, are here found in channels that are wholly sur¬ 
rounded by regions showing bowdders, glacial clay and gravel, 
and all evidences of ice action. Such incongruities are spe¬ 
cially striking at the’following places: 
McCoy’s Ford.Sec. 5, 
T. 85 N., 
R. 2 W. 
Table Rock. 
“ 36, 
44 87 44 
« 4 « 
Pulpit Rock. 
“ 25, 
44 87 “ 
u 4 u 
Wildcat Rock. 
44 24, 
44 87 44 
44 4 44 
Steamboat Rock.... 
“ 16? 
44 90 44 
4 4 6 44 
The last mentioned locality is at the resort 
known as the 
Backbone. Indeed, 
the Backbone 
itself is an example of this 
*See maps of Chamberlin and Salisbury, in the Sixth Annual Report 
of the U. S. Geol. Survey, plates 24 and 27 ; also McGee’s maps in the 
Eleventh Annual Report, plates 31, 44, 55, 56, 57. 
fU. S. Geol. Survey, Eleventh Annual Report, p. 391. 
