26 



ON THE GEOLOGY OF LOWER LOUISIANA 



Section of Red River Banks. 



Whether the upper portion of these profiles be of modern or ancient date, may 

 be a debatable question. The deposits now formed by E.ed River during its over- 

 flows are altogether predominantly of a light, loamy character Sheets of reddish 

 clay are, it is true, deposited locally by the back water, at the present time. But 

 the well-known rapid rise and fall of the river as it now exists, render it impos- 

 sible that a uniformity of deposits shoidd be maintained for any great length of 

 time in any given place, save along the main channels. Where newly formed 

 bayous cut through the modern cypress swamps, this rapid alternation in the nature 

 of the deposits may be seen as clearly as in the Mississippi bottom itself. In view 

 of these facts, it is impossible to escape the conclusion that the heavy, uniform clay 

 beds, continuous for miles, into which the river has cut its bed, owe their origin to 

 a state of things totally different from the present, and quite analogous to that 

 which gave rise to the clay beds at Port Hudson, and their wide-spread equivalents 

 on the Gulf coast 



It would be unreasonable to suppose, that the swampy inlets roughly representing 

 our present rivers during the Port Hudson period, were not traversed, more or less, 

 by definite channels carrying ofi" the rain-fall. Such channels would, doubtless, be 

 represented by beds of loam like that in profile No. 1, or, occasionally, by coarser 

 materials derived from the bordering hills. So for as I am aware, Red River in 

 Louisiana is not now knoAvn ever to carry gra\Tl in its main channel. Yet basin- 

 shaped beds of gravel do occasionally occur near low-water edge ; and in one ol 

 these (lying about a mile below profile No. 2, given above), which was considerably 

 consolidated, I found well-preserved fresh-water shells, such as Unio and Palmlina. 

 No locality from which these materials could have been derived occurs nearer than 

 six to eiglit miles, at right angles to the river. 



Not far below the locality last mentioned, we find in the bank one cf those 



