354 , GEOLOGICAL SURVEY OF THE TEERITORIES. 



water and land ; between the peat vegetation which tends to force 

 back the sea in building its moors, as ramparts against invasion, and 

 the marine force, searching an ingress, and in its charges scaling low 

 walls to re-occupy or farther extend its domain for a while. This, 

 of course, causes innumerable modifications of land-surface. The bor- 

 ings and shaftings around New Orleans record an alternance of forests, 

 either prostrated or standing, of gravel, of mud-beds, of peat, &c., as 

 a result of this coniiict, which, of course, becomes still more active and 

 varied near the mouth of our great rivers. The low bottom-lands of 

 the Arkansas and Eed Eivers at their entrance into the Mississippi 

 show the same kind of alternance in their stratification. The cause is 

 merely modified ; inundations, especially, marking their active influence, 

 instead of waves, tides, and currents. 



What has been said, as yet, tends already to explain not only the 

 cause of the multiplicity and variety of the deposits remarked in our 

 Lignitic and coal measures, but also the differences observed and re- 

 corded by experiments or analyses in the compounds of the combustible 

 minerals, not only at separate points of a same bed, but even on pieces 

 cut from the same block of moderate size. 



A perfect understanding, however, of the causes of all the differences 

 noted above, and other phenomena as yet unexplained in the formation 

 of coal and lignite, can be obtained only from the study of the mate- 

 rials which enter into the composition of a peat-bed, when seen on a 

 bank exposed in a vertical section. Such an examination can rarely be 

 made in this country, where the peat is as yet of comparatively little 

 value, and where the rare diggings are made by enginery ; heavy, 

 sharpened cutting-shovels, or boxes, moved by steam, bringing out the 

 matter from under water. The face of the banks is in that way con- 

 stantly immersed. In Europe, even now, peat is worked from large 

 banks isolated at first from the swamps and drained by canals. The 

 matter is cut by hand from the top to the foot of the banks, and on 

 these sections the difference in the compound resulting from variety of 

 the vegetation of the surface may be comparatively studied both ways, 

 either vertically for succession in time, or horizontally for distribution 

 of a contempoi'aneous flora. The examination of such banks of peats 

 shows at first that, even where the peat is older and more compact, one 

 can recognize and often count from the top to the bottom the layers of 

 vegetable matter which have been heaped each year for the constitu- 

 tion of the whole mass. Near the top the annual layers are spongy, 

 irregular, thick, varying from one to three inches ; by compression and 

 decay they become thinner by degrees, and at the bottom are some- 

 times reduced to one-tenth of the thickness of the surface-layers. They 

 show, too, irregularities resulting from the embedding of vegetables of 

 large size. Generally, however, the general growth is not entirely 

 stopped, even by prostrated forests. It is still indicated by thin layers 

 marking the remains of the vegetation of the Sphagnum^ and when, 

 either at once or successively, the trunks of trees become embedded, 

 there is for a while a kind of local confusion of the annual layers, till, the 

 growth of mosses and small vegetables having filled the intervening 

 spaces, the surface has become horizontal again and the layers distinctly 

 marked on wider areas. Generally, vegetable remains after a few years 

 are mostly rendered unrecognizalDle by compression and maceration, 

 which change their color and modify their characters, and, of course, 

 the older the peat-strata are the less their vegetable compounds become 

 identifiable. Some kinds, however, escape disintegration for an 

 immense space of time. These, like some species of mosses, of sedges, 



