Geology 



Navigation now became more difficult as the river 

 commenced to wind greatly, swinging now to right and 

 now to left in great loops in which there were many 

 shoals. These shoals consisted of masses of water-worn 

 gravel, and they always occurred on the inner sides of 

 the bends, while the deep water, accompanied by a steep 

 bank, was found on the outside of the curve. It was 

 now necessary to tie up the steamer for the night as it 

 was not safe to attempt to pass through this section 

 after dark. 



The meanders of a river are due to some obstacle, 



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... xx , 



ORIGINAL COURSE N x X N ^** 



SECOND COURSE ** X .-. -* +' 



THIRD COURSE * -^ 



FIG. ii. Diagram to illustrate the development of meanders. 



such as a large boulder or a fallen tree interfering with 

 the flow of the water as seen in Fig. n. An obstacle 

 being introduced at A, the stream is thrown across 

 to the opposite bank, as indicated by the arrows, 

 and at once commences to cut away the soft alluvial 

 deposits forming an embayment. The stream passing 

 round this curve is projected on to the other bank, which 

 it treats in similar fashion. In the meantime the current 

 at B, behind the obstruction, will be but slight, and 

 here sand and gravel will commence to accumulate, thus 

 forming a gravel bank such as we have already en- 

 countered. An examination of the arrows, which indicate 

 the direction of the current, will make it clear that matter 



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