National Geographic : 1897 Dec
THE DELTA OF THE MISSISSIPPI RIVER On page 2697 of the same report the commission itself con firms Mr Ockerson's statement by its own opinion, as follows: " The main object of this resurvey was to elicit some information bearing upon the question of the stability of the land about the mouth of the river. In the report of Assistant Engineer Ocker son, appended to the report of the secretary, a number of figures and comparisons are given, based upon this survey and prior ones, indicating a progressive depression of the alluvial delta near the mouth of the river." An interesting diagram, designed to show the changes referred to, assumes that either the tide gauge had gone down or the level of the Gulf had gone up over one foot in twenty years. Numerous pertinent facts might be brought forward to show, in addition to the above, that the lands had gone down and that the Gulf level had not changed. It is a fact well known to people living in the delta of the Mississippi that large tracts of land were long ago abandoned in consequence of overflow by Gulf waters, due to the sinking of the lands. The conditions are very different now from those existing prior to the construction of levees. There are at present no annual accretions of sedimentary matters from the periodical overflows of the river. These accretions formerly were a little more than equal to the annual subsidence of the lands. As to the question of the rising of the Gulf level, careful inves tigations and inquiries around the entire Gulf coast from Yucatan to Florida disclose no indications of any such elevations. The factors in forming the great hydraulic conditions of the Gulf op erate so steadily from year to year and from cycle to cycle that we should naturally expect that, with the exception of small an nual changes due to wind and tides, the mean surface of the Gulf would remain practically at the same level. The difference in precipitation, fluvial discharge into the Gulf, and evaporation is very slight as compared with the great current forces that make and maintain the Gulf level. From very careful observations, it may be stated that the mean precipitation, river discharge, and evaporation amount, all told, to a little over three cubic miles per day. This volume " sinks into utter insignificance when com pared with that produced by the inflowing current of the Yuca tan channel, which, according to a calculation from Lieutenant Pillsbury's current observations, hurls the enormous quantity of six hundred and fifty-two cubic miles of water per day into the Gulf."* *See a paper by A. Lindenkohl, Assistant U. S. Coast and Geodetic Survey, in Science, N. S., Vol. iii, No. 60, February 21, 1896.