THEORY. 189 



"As the river no longer rises over the meadows in time of floods, the process already 

 described is repeated, and a third terrace is the result ; and so a fourth, a fifth, etc., may 

 be formed, if the riA'er sink deep enough and time be given." 



Add to this drifting action of the current, the deposits brought in as deltas of the 

 various kinds of permanent and occasional tributaries, as previously explained, and we 

 have the causes of nearly all the lateral terraces explained. See too how the latter view 

 explains the slope and varying height and number. If the current of the stream had 

 produced a terrace, it must slope with that current, through its whole extent, as the sand, 

 etc., can never be brought above the level of the water, and must be brought near the 

 surface. And in regard to the number and equality of the terraces on the two sides, we 

 see that the energy of the current is principally devoted to one side of the stream ; 

 consequently but one terrace would form ; and as the land was slowly rising when the 

 stream began to deposit upon the opposite side, the top of the terrace would be lower than 

 the one previously formed ; though the difference would probably be but a few feet. 



It is thus that we see the reason why a single high terrace may exist upon one side of 

 a valley opposite to four, five or six. The current has always made its deposits, except in 

 one instance, upon that side where the terraces are most abundant, and this change in 

 number, height, &c., upon most streams, will vary with every prominent bend in the river. 



We see also from this view why the terraces about gorges may be higher than those in 

 the widest part of the basin. The contraction of the stream at the gorges would check 

 the current, and thus cause more of the suspended matter to be deposited. Very proba- 

 bly it might so fill up the gorges, that as the continent rose it would require a great length 

 of time to wear them down to their present depth. 



9. Thus we have seen that the various forms of river terraces may be produced by the 

 simple drainage of the country, as the surface emerged from the ocean. The methods by 

 which the terraces were formed may sometimes have varied from those described, and 

 wherever it seems necessary we should call in the aid of all the modes proposed. Nor is 

 it necessary to suppose that there were pauses in this vertical movement. Such pauses 

 may have existed, and in this way there may be certain determinate successive levels at 

 which beaches and terraces are found but to form the river terraces we need not call in 

 their aid. 



10. We can proceed further, and show that river terraces in general could not have been 

 produced by pauses in the vertical movement of the land. 



1. If thus produced, they ought to be the same in number and in height in the different 

 basins of the same river ; and if the whole continent was affected by the same paroxysm, 

 all the terraces upon it ought to be subject to this law. Even though a slight difference 

 in them be admitted, their number must correspond, since the water would sink equally 

 in the different basins. But upon examining the different sections of terraces on previous 

 pages, it will be seen that there is no such agreement. On the Connecticut four and five 

 are common, but not unfrcquently the number increases to six and sometimes seven, 

 and almost every section presents a different scries of heights. Upon the tributaries, 

 we see the number frequently rise to ten. Which of these numbers shall be assumed 

 as indicating the number of pauses in the vertical movement ? If the smallest, then how 

 are we to explain the excess ? If the larger number, then why did not the waters leave 

 traces of their influence alike numerous wherever they acted an equal length of time? 



