GEOLOGY OF SOUTHWESTERN IOWA. 337 



a summit region in relation to the drainage of the sur- 

 rounding country, and yet, nnlike many similar summit 

 regions, it is so perfectly drained that ponds and marshes 

 are nowhere to be fonnd. 



Like all the other counties that lie npon the Great Water- 

 shed, the drift of Adair county is very deep, probably two 

 hundred feet deep in its central portion. Therefore, with the 

 exception of that of Middle river, all its valleys are true 

 drift valleys, and even that of the river named is only 

 slightly modified by the few exposures of strata that occur 

 along its course. Some of these valleys reach a depth of one 

 hundred and fifty feet from the general level of the upland, 

 and yet nothing but drift is to be seen within them. 



The surface of Adair county, although almost all prairie, 

 is very undulatory, and in many parts is quite broken by 

 deep, yet grassy ravines. This un evenness of surface 

 renders a part of it untillable by the ordinary methods 

 now T in use. The soil of these steep slopes, however, is 

 almost as fertile as that upon the more level surfaces, 

 and the time will come when they may be cultivated with 

 profit. Much the larger part of the surface of the county 

 possesses not only an excellent soil, but it is also adapted 

 to convenient tillage. The drift of this county, like that of 

 the others adjoining it, is almost entirely composed of com- 

 paratively fine material, so that the surface is never 

 obstructed by boulders, or other impediments to agricul- 

 tural operations, yet a few isolated boulders occasionally 

 appear. A number of these granite strangers from the 

 north are to be seen upon the surface near the head of 

 Grand river, in the eastern part of the county. 



Geology. The only strata exposed in this county are found 

 in the valley of Middle river, and consequently are confined 

 to the eastern and northeastern portions. These all belong 

 to the Upper coal-measures; and, judging from our know- 

 ledge of the geology of the surrounding region, the same 

 strata occupy the remainder of the county immediately 



beneath the deep deposit of drift, unless, which is possibly 

 43 



