352 THE DELTA OF THE MISSISSIPPI RIVER 



Many interesting facts bearing upon the question of the geo- 

 logical formation of the Mississippi delta were brought to atten- 

 tion two years ago through the investigations and discussions 

 connected witli an engineering question which arose l)etween the 

 executors of the late Mr James B. Eads and the War Department 

 as to what is the legal plane of reference for ascertaining the 

 depths and widths of channel which Mr P]ads was required by 

 the law of the Federal Congress to maintain between the deep 

 water of the South Pass of the Mississippi river and the Gulf of 

 Mexico. 



On Belize bayou, which leads out to the Gulf from one of the 

 now unused passes of the river, stands an old Spanish magazine, 

 built over 200 j^ears ago. At the time of building the jetties at 

 the mouth of the South Pass this magazine was in a fair state of 

 preservation. The exterior was intact and there were no cracks 

 which would indicate settlement, the building standing perfectly 

 level, but with the surface of the water stretching across the arch 

 which crowned the entrance door, the sill of which must have 

 been at least ten feet below the water. That was in the year 1877. 

 Nineteen years later a part of the structure had been removed, 

 but enough of the roof and arches remained tp show that the 

 subsidence had continued steadily during that period of nine- 

 teen years at about the same rate as during the preceding two 

 hundred years. It may be stated that this rate, both from this 

 instance and from other information, is, at the mouth of the 

 Mississippi, about one-half of one-tenth of a foot per annum. 

 Numerous illustrations going to prove the general subsidence 

 of the delta lands might be stated. Not only are these lands 

 unstable in a vertical direction, but they are often found to be 

 so in a lateral direction. It is an interesting engineering as well 

 as physical fact that an accurately measured base line exactly 

 seven hundred feet in length was found, after a lapse of five years, 

 to be 712 feet in length. It has been found impracticable to 

 maintain with sufficient accuracy for reference purposes bench- 

 marks, level heights, and tide gauges. This subject is quite 

 fully discussed in the Report of the Mississippi River Commis- 

 sion for 1894, pages 2794-2797, where the following important 

 statement is made : " Discrepancies in bench-marks and level 

 heights and gauges could only be satisfactorily accounted for 

 by the most plausible explanation of the subsidence of the whole 

 delta, making gauges and bench-marks at the mouth of South 

 Pass unreliable." This remark is made by Mr J. A. Ockerson, 

 assistant engineer to the commission. 



