QUATERNARY AGE. 297 



ent that the period of its formation must have been very long. There 

 -are still some few localities where that formative condition has been 

 perpetuated to the present time as, for example, the bogs that are 

 yet met with at the head-waters of the Elkhorn and the Logan, 

 along the Elk Creek, on the Dakota bottom, and on the Stinking 

 River, one of the tributaries of the Republican. In fact, along these 

 tributaries all the intermediate stages from perfectly dry bottom to 

 a bog can yet be found. But, so much has the volume of water 

 iDeen lessened in all the rivers of Nebraska through the influence of 

 geological causes, that there are few places where now, even in 

 flood-time, they overflow their banks. A curious phenomenon, il- 

 lustrating through what changes of level and other conditions these 

 river bottoms have passed, before reaching their present form, is 

 the occurrence at various depths, of from ten to fifty feet, of great 

 masses of timber in a semi-decayed condition. One such deposit on 

 the Blue River bottom, near the mouth of Turkey Creek, success- 

 fully interrupted the digging of a well. So many thicknesses of logs 

 occurred that it was found best to abandon the work already done for 

 a new place. I have frequently observed trees, with trunks twenty 

 to sixty feet long, sticking out from under the banks of the Mis- 

 souri, where the soil had been freshly removed. It is possible that 

 this timber accumulated in these places during the period when the 

 rivers yet covered their entire bottoms, and when numberless trees 

 must have been carried down during flood-time, and either stranded 

 on the ancient sand bars and mud-banks, or sunk to rise no more in 

 the deeper pools and eddies which were rapidly filled up. The 

 species, so far as I have yet been able to determine, from an exam- 

 ination of the half-decayed wood, are the same as yet grow in this 

 region. They are principally cottonwood, elm, cedar, maple and 

 walnut. 



THE SAND-HILLS. 



The sand-hills are an often-mentioned portion of Nebraska. 

 'They are found in certain sections of the western portion of the 

 State. South of the Platte Valley they run parallel with the river, 

 and are from one-half to six miles in breadth. A few are also 

 found on the tributaries of the Republican. Occasionally slightly 

 sandy districts are found as far east as the Logan, but they rarely 

 approach even a small hill in magnitude. A few sand ridges are 

 also found on the Elkhorn. North of the Platte, from about the 

 mouth of the Calamus on to the Niobrara, they cover much larger 



