88 Observations on Terraces. 



been a sea-beach? And at the mouth of the Ohio, will the 

 height of the terrace plane above the sea be a measure of the ele- 

 vation that took place ? Terraces of the same epoch would ex- 

 tend up the Mississippi more or less interrupted, another 1000 

 miles and beyond ; and the height above the sea, if the measure 

 of the elevation, would prove an increase northward, while the 

 actual fact might be a uniformity throughout, or even a some- 

 what less elevation to the north. The formation of wide bottom 

 lands from such a cause cannot be doubted, for their actual exist- 

 ence about nearly all rivers proves it ; other considerations may 

 hereafter be brought forward by the writer to illustrate this 



subject.* 



The point to which I would now direct attention is one of 

 fundamental importance in these investigations. It is this : 

 The deposition of the stratified material which is terraced, and 

 the formation of the terrace plane and slope, are not necessarily 

 of like origin. 



Whatever be the nature of the material that constitutes the 



Mississippi region, whether river detritus, accumulations by gla- 



cier action, or a filling in from the sea while the land was at 

 a lower level, the river would flow on as now ; and if an ele- 

 vation were to take place, the material existing there would be 

 terraced, whether of one or the other origin. As above explained, 

 there might be terraces of river origin, although the material were 

 from a marine or glacial source : and the evidence from the ter- 

 races with regard to amount of elevation would be the same in 

 either case. Hence the question of the origin of the material 

 and that of elevation are in part distinct. There may be river 

 terraces, therefore, with the deposits either fresh or marine ; but 

 it still holds that those of sea-beach origin must admit of proof 

 to this effect from some character, manifest in one place or an- 

 other in the course of a distance of one or two hundred miles. 



Here then is another point, complicating still farther the inves- 

 tigations respecting terraces. In the discussions upon drift, 

 which have referred in part to the very material that constitutes 

 the upland terraces — geologists are divided among the following 

 theories. 1. That of marine transport during submergence ; — 2. 

 that of marine transport over the emerged land, in consequence 

 of violent earthquake action ; — 3. that of lacustrine or river ori- 

 gin ; — 4. that of glacier origin; — 5. (as we recently learn) that 

 of sea-beach origin : — and the arguments for each hypothesis are 

 strongly urged. It is hence obvious that there is the highest ne- 

 cessity, before deciding upon these subjects, that every possible 

 aid in search of truth be employed. 



See Report by the writer on GeoL ExpL Exped., pp. 659, 671. 



