QUATERNARY AGE. 257 



Drift below. Here, as in most other regions, the Drift varies a 

 great deal in character. As already intimated, it has here been so 



modified by subsequent lacustrine agencies as generally to be ca- 

 pable of high cultivation. Recently I have made a special exam- 

 ination of the modified Drift in Johnson County. Where the 

 ground was covered with pebbles, the spade showed that the soil 

 beneath was composed largely of Loess materials, mixed with 

 Drift sand and clay, and organic matter. Here it is often in layers, 

 showing that it is genuine modified Drift. This modified Drift 

 soil, during the last season, where it was well cultivated, yielded 

 sixty bushels of corn to the acre. It is only inferior, if inferior at 

 all, to the Loess, which will be considered in the next section. 

 Where this Drift is the purest, it is composed of boulders, some of 

 which are of large size, pebbles, gravel, sand, and a small per cent 

 of alumina. In places the Drift contains considerable lime, which 

 was, no doubt, produced by the disintegration during glacial times 

 of the Niobrara division of Cretaceous rocks. Sometimes frag- 

 ments of these Cretaceous rocks are found in the Drift. Generally 

 the pebbles and boulders are composed of the primary rocks, such 

 as quartz, quartzose, granite, greenstone, syenite, gneiss, porphyry, 

 actinolite, etc. Occasionally the year presence of the Drift is indi- 

 cated by large boulders sticking up through soil composed of very 

 different material. In such cases I have learned by experience to 

 look for the modified Drift, which is so valuable in the agriculture 

 of this State. In the few localities where all the finer matter has 

 been removed by water agency, numbers of the different forms of 

 variegated agates, carnelians, jaspars, sardonyx, onyx, opals and 

 petrified wood, etc., are found. Agates and petrified wood are 

 specially abundant. The latter is found almost in every exposure 

 of the Drift. Some of the agates vie in beauty with those obtained 

 from the most celebrated localities in the mountains. Judging from 

 the remains of the matrix still attached to some of them, they were 

 originally formed in the secondary rocks, from which they were 

 separated by the disintegration to which they were subjected by 

 the wear and tear of the elements in glacial times. 



A brief description of a remarkable section through the Drift on 

 Oak Creek, Lancaster County, will not be out of place. A few 

 miles from Lincoln the terrace on this creek, composed of Loe-- 

 materials, approaches the creek very closely. In this well the 

 Loess deposit was fifteen feet in thickness, then came two feet of 



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