328 T. C. CHAM BERLIN 



larly characteristic of streams subject to great variations of 

 vigor, as for example streams in regions of alternating dry and 

 wet seasons, as in the Vero case, especially when heavy rains are 

 frequent and even typhoons are occasional. This scour-and-fill 

 action is a special mixing process superposed on the more general 

 ' ones already sketched. 



Now if, in the case in hand, only a foot or so be allowed for 

 the flood-plain deposits in process of growth, and only a foot or 

 so for the normal channel-work, and only a foot or so below that 

 for the deeper scour holes here and there, the vertical range of 

 this active formative and reworking process is too great to be 

 neglected when there are only six feet of deposits altogether to 

 be dealt with. It must be kept in mind that this working com- 

 bination, now at the top, has in the process of forming the six- 

 foot deposit gradually worked up from the bottom, leaving some 

 portion of its base at successive stages to help build up the lower 

 part of the six feet. This lower part is thus an accumulation of 

 residues from the working combination. 



It is therefore necessary to distinguish between the working 

 group at the top — which in the case in hand ceased its formative 

 process in 19 13 — and the succession of residual deposits below it, 

 these being merely the truncated bases of the formative deposits 

 which the successive meander-shears have left behind. The group 

 in process of formation at the top belongs not so much to the 

 Recent Period as to the current working stage. Setting this aside 

 as merely the record of the work in progress when suspended, 

 how much more is to be added from the rest of the six feet below 

 to make up a reasonable record of the past two hundred centuries, 

 more or less, which, according to our tentative scale, constitute 

 the Recent Period? Will anything less than the two or three 

 feet of the upper layer. No. 3, suffice ? Indeed, is that enough ? 



This method of proceeding from the known to the unknown 

 seems eminently sound and helpful up to this point; here it 

 encounters difficulties and these show its limitations. Theoreti- 

 cally, the several basal accretions left by the successive meander- 

 shears may (i) have some notable thickness, (2) or very little 

 thickness, or (3) even a minus thickness, i.e., there may be loss 



