tween the piers of the bridge at St. Louis, in filling, or scouring, 

 the bottom as the river rose and fell, or carried a greater or less 

 load of sediment with the change in the velocity of the current, 

 had confirmed him in the certainty of his conclusions. 



December i, 1S73. 

 The President, J. B. Eads, in the chair. 



Twenty-two members present. 



The Corresponding Secretary laid upon the table several pub- 

 lications received, and among them a pamphlet by Col. C. G. For- 

 shey of Louisiana upon the " Delta of the Mississippi River." 



Judge Holmes observed that Col. Forshey was of the opinion that the 

 proper delta of the Mississippi extended up to within a few miles of Cape 

 Girardeau in Missouri, though Sir Charles Lyell had taken the head of 

 the Atchafalaya branch below Natchez as (geologically speaking) the hetfid 

 of the delta. In one sense, he was inclined to think Col. Forshey might 

 be correct. The present configuration of the land showed a valley having 

 its apex just below Cape Girardeau and expanding in width below to thirty 

 and ninety miles (or say an average of sixty miles) between the highlands 

 on either side. This whole valley, now an alluvial plain, had evidently 

 been filled up by alluvial deposits from the river to a greater or less depth. 

 In the Tertiary period, the Gulf had certainly ascended this valley thus 

 far. This fact was proved by the existence of Tertiary deposits in South- 

 eastern Missouri, and in Southern Illinois, at no great distance from the 

 Mississippi and the Ohio. Since that time, there had been, not only a 

 considerable elevation of the land, but some change in the level of the con- 

 tinent. This was proved, not only by the known upheaval of the Rocky 

 Mountains in the Tertiary period, but by the fact that, as late as the Qua- 

 ternary, a great inland fresh-water lake, or expansion of the Mississippi 

 and Missouri rivers, existed, having the ridge crossing at Grand Tower 

 as its probable southern barrier, and extending far up the Mississippi and 

 its tributaries. The extent of this lake is evidenced by the extent of the 

 fresh-water deposits or Loess. And now, if the existing elevations at 

 Omaha, Kansas City, Quincy, St. Louis, Grand Tower, and the mouth of 

 the Ohio, be taken into consideration, it will be apparent that the existence 

 of such an inland fresh-water lake would be impossible with the continent 

 at its present levels. A change of level is, therefore, quite certain; and, 

 during this change, it is probable that the barrier at Grand Tower was 

 gradually cut down, and the lake drained off. This is analogous to what 

 happened on the Columbia river, and on other great rivers of the globe. 



