CHAPTER XIV. 



ORIGINAL STRUCTURE AND LITHOGENESIS OF THE CONTI- 

 NENTAL HYDROCLASTICS. 



A very large, perhaps the largest, portion of the stratified elas- 

 tics of the earth's crust consists of water-laid deposits, or hydroclas- 

 tics. By this is not meant that they were deposited in standing 

 water, though this is true of a large portion of them, but that water 

 was influential in the making of the deposit. They therefore include 

 river-laid elastics as well as those formed in the sea or in lakes. 



Hydroclastic rocks may be divided into the following groups : 



1. Stream or river-laid elastics (potamoclastics). 



2. Lake or lacustrine elastics (limnoclastics). 



3. The Delta — a transitional deposit. 



4. Marine elastics (haloclastics). 



Each of these will admit of a number of subdivisions. The 

 potamoclastics and limnoclastics, together with the atmoclastics, 

 anemoclastics, pyroclastics, and autoclastics belong to the continen- 

 tal or terrestrial type of elastics, as opposed to the marine or halo- 

 clastics. Seacoast deltas form the transition from the one to the 

 other. The continental hydroclastics, together with the delta de- 

 posits, will be considered in this chapter ; the marine hydroclastics 

 being reserved for the next. 



RIVER-LAID CLASTICS, OR POTAMOCLASTICS. 



All along the river course, from near the head to the mouth, 

 clastic deposits may be forming, their character and amount vary- 

 ing with the character of the stream and its environment. Under 

 the latter, the kind of rock material and climate must be mentioned 

 as all-important controlling factors. The amount of weathered 

 rock material available for transport and final deposition is also 

 of the greatest importance. We may consider the clastic river~ 

 deposits under the following headings : 



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