488 A. Tylor — Formation of Deltas. 



employed in favour of Bubsiclence, and producing elevation in balance ; 

 for instance, the conversion of a dry valley into a lake must tend to 

 lower the earth's crust by its extra weight, tending to produce sub- 

 sidence at one point and elevation at another. Any delta deposit 

 would tend to produce subsidence. The depression of the Channel 

 must have lowered a much larger mass, apart from volcanic 

 energy, than the Wealden elevation raised. In the opinion of the 

 author, all elevations are uneven and sudden. The elevation of 

 the Alps in the Miocene period must have accompanied or been the 

 consequence of a much larger movement of depression; probably at the 

 time a Miocene island or continent (near Plato's Atlantis) in the Atlantic 

 was suddenly depressed. E. Forbes thought the position of the great 

 floating masses of sea- weed marked the site of this ancient land. A 

 subsidence of solid matter in one part may displace fluid or gas, on 

 Sir H. Davy's theory, and produce an elevation of solid matter to an 

 equivalent height elsewhere ; but it cannot produce a corresponding 

 elevation elsewhere (as part of the force is expended without pro- 

 ducing motion), except where there is a fluid, or the equivalent of a 

 fluid (as in the Delta of the Mississippi), to communicate movement 

 without loss of energy, or below the surface of the solid crust where 

 matter may be fluid. 



In concluding my remarks upon the Delta of the Eiver Po, it is 

 only necessary to repeat that it is shown in the diagram Fig. 1, 

 by the strata, A. and B., that there are two principal beds which 

 are always water-bearing, one between the limits of 145 and 181 

 feet, and the other at about 200 feet. The upper sand bed, B., is so 

 full of carburetted hydrogen gas, that in applying a light to the 

 mouth of some of the wells the gas first detonates and then continues 

 burning with a constant flame. The lower sand bed contains less 

 gas, but is always full of water, which flows with great regularity. 



The writer exhibited at the Geological Society a drawing by Mr. 

 Jenkins of some of the Eocene Cyrena beds, with plants, etc., which 

 prove that at Dulwich a deposit like that of the Delta beds of the 

 Po existed in Eocene times. 



Delta of the Mississippi. — A somewhat similar bed of sand exists 

 in the Delta of the Mississippi, near New Orleans, at a depth of 60 

 feet from the surface. This has been tapped in many parts of New 

 Orleans for the carburetted hydrogen gas it contains. Iron tubes, three 

 or four inches in diameter, are forced down 60 feet, and the gas is suffi- 

 ciently good for burning. I will now give an abstract of the description 

 which has been published, of the section of a well, by Dr. Bendict. 



The well, commenced in New Orleans in 1854, was only continued 

 to a depth of about 630 feet. There are 36 well-marked alterna- 

 tions of clay and sands ; 4 lignitiferous beds, some with rootlets, and 

 the lowest at 150 feet from the surface containing a sound cedar log 

 striated with thin plates of siliceous matter. There are 6 shell-beds 

 in different parts of the series of marine and fresh water-beds ? 

 making a total of 14 feet. The lowest. No. 54, was 543 feet from the 

 surface. The 18 beds of clay make a total thickness of 266 feet. The 

 lowest of these is 36 feet thick, and is No. 65 in the series. No. 53, 



