Page:Popular Science Monthly Volume 43.djvu/266

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the tidal currents with an unfailing supply of muddy sediment. It is mainly in the erosion, transportation, and reprecipitation of these two rocks, and especially of the latter, that the process of marsh formation consists. The incessantly destructive tide-work may be seen at many points along the shore line, perhaps most conspicuously at the base of Blomidon. Here the sandstone foundation is continuously being cut away from under the super-incumbent columnar trap; and at intervals, especially in the spring time, large masses of the igneous rock are loosened from the precipitous mountain side and crushed upon the beach below, where the solvent and abrading action of the waters can reach them. It is after one of these spring slides that the richest harvests of amethystine and zeolitic crystals, for the beauty and abundance of which the Minas shores are noted, can be secured. But it is along the bottom of the bay that the destructive tidal work is most extensive and effective. Here exist great troughs, furrowed out of the soft sandstone, many fathoms deep along the channel bed, with here and there the interruption of the transverse trappean dikes already spoken of.

The sandstone yields, of course, the greater part of the marsh-creating sediment. Its detritus consists of a large percentage of silica, a little clay, the iron which mainly determines its reddish color, and the calcareous matter which served as cement in the parent rock. This material, in the extremely comminuted form in which it occurs in marsh-land soil, would itself afford conditions highly favorable to the support of vegetable life. But an additional cause of the wonderful fertility of the Acadian marshes is the richness of the trap rock in various salts of potash, lime, and alumina which the action of the water mingles freely with the sandstone mud. The plant-supporting power of this complex soil is increased still further by contributions from the upland soils through the medium of the streams and rivers flowing toward the bay.

The great fertility of this alluvium may be inferred from the fact that portions of the Annapolis, Cornwallis, Grand Pré, and Cumberland marshes have been producing annually for nearly two centuries from two to four tons per acre of the finest hay. Besides, it is a common practice, after the hay has been removed, to convert the marshes into autumn pastures, on the luxuriant tender after-growth of which cattle fatten more rapidly than on any other kind of food. Thus, virtually, two crops are annually taken from the land, to which no fertilizing return is ever made. The only portions of the Acadian marshes that have as yet shown signs of exhaustion are those about the Chiegnecto branch of the bay, on the cliffs and bed of which the Triassic rocks do not occur, but in their stead a series of blue and gray "grind-