258 



GEOLOGICAL SURVEY OF THE TERRITORIES. 



Insoluble (siliceous) matter 



Ferric oxide 



Alumina 



Lime, carbonate 



Lime, phosphate 



Magnesia, carbonate 



Potash 



SoJa. 



Sulphuric acid 



Organic matter 



Loss in analysis 



63.07 



2.85 



8.41 



7.08 



.90 



1.41 



.50 



.49 



.79 



14. 00 



50 



100. 00 



63. 70 



2.25 



7.76 



7.99 



.85 



1.45 



.54 



.52 



.70 



13. 45 



.79 



100.00 



63.01 



2.40 



8.36 



8.01 



.99 



1.39 



.61 



.54 



.71 



13.01 



.97 



100.00 



62 99 



2.47 



8. 08 



7.85 



94 



1.40 



.67 



.58 



.79 



13.27 



.96 



100.00 



No. 5. 



61.03 



2.82 

 10. 52 

 7.09 



.98 

 1.38 



.60 



!<59 



13.40 



.92 



It is well known that many soils vary a great deal in chemical prop- 

 erties that are taken only a few feet apart, and therefore analyses often 

 fail to give a correct idea of their true character. But from the above 

 analyses, taken from widely distant localities, it is at least evident that 

 chemically, alluvium differs from the Loess deposits, principally in having 

 more organic matter and alumina, and less silica. The depth of the 

 alluvium varies greatly. Occasionally sand and drift materials predomi- 

 nate in the river-bottoms, especially in the subsoil ; sometimes the allu- 

 vium is of unknown depth, and again in a few feet the drift pebbles 

 and sand of the subsoil are struck. This is especially the case in some 

 of the western valleys which were worn down to the drift, and were 

 not again subsequently filled up, though such cases are not often 

 met with. There must have been a period of longer or shorter 

 duration, when the bottoms were in the condition of swamps and 

 bogs; and during this period the greater part of that organic mat- 

 ter, which is a distinguishing feature of these lands, accumulated in the 

 surface-soil. It would be easy to select isolated spots, where the soil 

 has forty per cent, of organic matter ; where, in fact, it is composed of 

 semi-peat. When we reflect that this black soil is often twenty feet 

 thick, it is apparent that the period of its formation must have been 

 exceedingly long. There are still some few localities where that forma- 

 tive condition has been perpetuated to the present time — as, for ex- 

 ample, the bogs that are .vet met with at the headwaters of the Elk- 

 horn and the Logan, along the Elk Greek, on the Dakota bottom, and on 

 Stinking River, ono of the tributaries of the Republican. In fact, along 

 these tributaries all the intermediate stages from perfectly dry bot- 

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

 been lessened in all the rivers of Nebraska through the influence of geo- 

 logical causes, that there are few places where now, even in flood-time, 

 they overflow their banks. A curious phenomenon, illustrating 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 Greek, successfully 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 ob- 

 served trees, with trunks twenty to sixty feet long, sticking out from un- 

 der the banks of the Missouri, 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 num- 

 berless 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 



