INVESTIGATION VERSUS PROPAGANDISM 2>^'j 



titude of individual cases involved; the mixed product thus 

 comnionly shows a wide range of variation. In part the mixing 

 may be very gentle and the hard parts in the muck may show 

 very slight abrasion. The slide of the muck banks into the bed 

 of the creek is often one of the gentlest of moving processes, for 

 the muck lubricates and cushions the sliding mass. The matter- 

 enveloped in the muck, however weak it may be, is easily slipped 

 along in its cushion without appreciable strain or abrasion. Muck 

 balls may even be formed and rolled notable distances, carrying 

 in their protecting embrace structures of any degree of fragility 

 until burial shall finally fix them in the stream sands or disintegra- 

 tion shall free them for a cleaner burial in the same sands. The 

 typical channel material in the stricter sense, that is, the material 

 which has been rolled along the stream bed for considerable dis- 

 tances, perhaps from sources beyond the aggradational tract, is 

 normally much more worn, whether it be rock or bones. The 

 several parts of the creek, deposit are thus likely to show the 

 eft'ects of very different experiences. Only a critical study of 

 each individual relic is usually sufficient to disclose its special 

 history. Normally there is a very wide variation of conditions 

 ranging from relics that remain almost intact to those which are 

 very much abraded. 



Now it is the normal habit of a stream that meanders on a 

 plain of its own formation to shift its channel gradually down- 

 stream by undercutting or eroding its banks preponderantly on 

 the down-stream side. In the course of time the stream thus 

 slowly creeps over its whole flood-plain, and in so doing cuts away 

 and reworks a large part of the flood-plain deposit. As the 

 meanders thus slowly shear their way over new ground, new 

 flood-plain deposits are formed on the ground abandoned by them ; 

 thus the flood-plain .is rebuilt behind the shearing meander and 

 made ready to be cut away again when the next meander reaches 

 it in its progress down-stream. 



Now, as already noted, this shearing process is attended almost 

 inevitably by the special supplementary work of scour-and-fill 

 which bores its holes below the common channel-level at the 

 points of specially forceful or turbulent action. This is particu- 



