COLLUVIAL DEPOSITS 307 



Deposits of the cumulose type pass by all gradations into 

 the paludal, swamp, or marsh type and these in turn into ordi- 

 nary alluvium. Or it would perhaps be better to reverse this 

 order, since, as in the gradual silting up of an enclosed lake, 

 we may have, in the first stages, stratified alluvium, then when 

 the waters become sufficiently shallowed, swamp and muck 

 deposits, and lastly the deposits of pure organic, or cumulose 

 material. 



2. TErAlTSPOIlTED MATERIALS 



Because of the constant action of gravity, the well-known 

 transporting power of water, the wind or moving ice, few re- 

 sidual products retain for any length of time their virgin purity, 

 but become more or less contaminated with materials from near 

 or distant sources. The avalanches of mountain regions afford 

 an illustration of the bodily transfer of, it may be, millions of 

 tons of matter from the mountain slopes to be debouched into 

 the valley below; the slow-creeping glacier brings down its 

 load and deposits its moraine when, succumbing to the blan- 

 dishments of warmer climes, it is no longer able to bear it fur- 

 ther : spasmodic winds catch up the smaller particles as clouds of 

 dust to be transported, assorted, and redeposited, as their force is 

 spent. It is, however, through running streams, both in the past 

 and present, and moving ice in ages gone, that has been brought 

 about the great amount of transportation and admixture charac- 

 teristic of that part of the regolith comprised under the general 

 name of drift. According to which of the agencies enumerated 

 prevailed, the resultant products may be classified as follows: 

 (1) Colluvial deposits, (2) alluvial deposits, (3) geolian de- 

 posits, and (4) glacial deposits, though it will be found that the 

 lines of separation are' not in all cases sharply drawn, and in 

 many an area the regolith bears impress of compounded agencies. 



(1) Colluvial Deposits.^ — Under this head it is proposed to 

 include those heterogeneous aggregates of rock detritus com- 

 monly designated as talus and cliff debris. The material of 

 avalanches may also be classed here. Such result from the trans- 

 porting action of gravity. The deposits in themselves are com- 

 paratively limited in extent, ever varying in composition, and are 



^ From tlie Latin ' ' colluvies, ' ' a mixtuTe. The term as here used is more 

 restricted in its meaning than as defined by Professor Hilgard 



