. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 376 THE EEGOLITH period, when plants of tlie lycopod type appeared. Such soils, as soils, have, however, long since disappeared in the never- ending cycle of change, and it is not until we reach the Car- boniferous period that we meet with soils which have been preserved in place and in recognizable form even to the present day. Even here induration and partial metamorphism has rendered them no longer fitted for the support of plant life, but that they once did so serve is amply proven by the occa- sional finding of erect, fo
. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 376 THE EEGOLITH period, when plants of tlie lycopod type appeared. Such soils, as soils, have, however, long since disappeared in the never- ending cycle of change, and it is not until we reach the Car- boniferous period that we meet with soils which have been preserved in place and in recognizable form even to the present day. Even here induration and partial metamorphism has rendered them no longer fitted for the support of plant life, but that they once did so serve is amply proven by the occa- sional finding of erect, fossil tree trunks with roots buried in their native soil, as they grew in the marshes and woodlands of the coal period. But as to the time of the beginnings of the formation of such soils as still retain their soil characteristics, we have not in all eases reliable data. Those which are but the unconsolidated sediments of recent geological time, like those of the eastern shore of Mary- land, the loess and alluvium of the Mississippi valley, or the swamp and glacial soils of the north and east may, of course, be located with a rea- sonable amount of accuracy. But as for the residual soils, those which result from the breaking down in place of rock masses, we can only say that they must be younger than the rocks from which they i^ ^^:t^JiS^^--f Pig. 38.—Trunk of tree stiU standing in soil of Carboniferous age. a, becl-Tock; hf under clay or ancient soil; c, coal J dj bedded rock; e, fossil tree. were derived. The writer has shown that the granite soils of the District of Columbia are post-Cretaceous; in other parts of the Piedmont plateau of Maryland, they may be post-Tertiary. In but few instances, as at Medford in Massachusetts, have we evi- dence of any considerable amount of soil formation by decom- position and disintegration since the close of the glacial period. Obviously the older a residual soil, the greater the amount of de- composition and leaching it will have
Size: 2570px × 973px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectpetrolo, bookyear1913
