Page:Popular Science Monthly Volume 45.djvu/880

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THE POPULAR SCIENCE MONTHLY.

is this habit fixed, however, that, even where a tree stands alone, its trunks and branches are almost invariably covered with these plants. Their abundance and variety may be judged from the fact that upon a single jicara tree, not more than twenty feet high, which stood in a clearing near Castillo, the author counted forty species of epiphytes. The vines and underbrush are less abundant on the higher grounds, and moving about is consequently easier. But, whether the place is high or low, the same deep, dark, reeking forest spreads over all. Two facts strike the observer as peculiar, at least during the season which the party spent at Castillo—the comparative scarcity of brilliant flowers, and the failure of the plants of one species to mass together. The comparatively small number of conspicuous flowers is a disappointment to him who expects to find a mass of brilliant bloom in these tropical forests; not so much because these flowers are really wanting as because the flowering period of most of the species is rather long, and for the further, perhaps more important, reason that the flowers which do appear seem insignificant when compared with the sea of green that covers everything. No less striking is the fact that, as a rule, specimens of any one species do not mass together to the exclusion of other species, excepting sometimes along the watercourses. Different kinds of trees are mingled together m endless confusion, and no "groves" of any one species, such as we are familiar with in the North, occur, nor can any species, as a rule, ever be said to be prominent. The same is true of smaller plants; and the collector is not only bewildered by the variety of plants that come in his way, even in a restricted locality, but is also provoked by the scarcity of specimens of most of the species. Along the river banks, however, palms, grasses, etc., often take possession of large tracts.

 

Origin of Clays.—Clay, says Mr. Robert T. Hill, in his report on that material in the "Mineral Resources of the United States," is the immediate or ultimate product of the decomposition of feldspar. Feldspar is a constituent mineral of all the igneous rocks of the earth, and is especially abundant in the older granites and gneisses. By its decomposition, which occurs principally under the action of water, the soda, lime, potash, and other alkaline constituents of the feldspar are removed in solution, leaving the aluminum silicate and quartz as a residuum, commercially known as rock kaolin—a non-plastic material which, when free from iron, is also known as porcelain clay. Water, in Nature as in pottery, is the chief agent in clay working, and, besides its original action in decomposing the feldspar, it transports and grinds the original kaolin, and deposits it, in various degrees of purity or mixture, in secondary localities as a sediment. Clay material thus produced is known as sedimentary or transported clay, and, with the exception of some of the kaolins which have not been far removed from their place of origin, is more or less plastic. The washing and grinding of clays by clay-workers is a repetition of fundamental geologic processes of erosion, corrosion, and deposition constantly going on in Nature; and the geologist can see in the flumes and settling tanks of the potter a laboratory demonstration of the principal agencies which he studies. The clay material resulting from the decay of feldspar may be broadly classified under the two general heads of residual and sedimentary. The residual material is that which is found in the original place of occurrence of the decomposing feldspar, and may possess many physical aspects, sometimes occurring as a firm or crumbling rock, resembling decomposed granite, or again as a fine, white, non-plastic clay or kaolin. It is usually accompanied by quartz, a material not essentially injurious, which can be removed, if that is desired, by washing. The sedimentary clays are those which have been removed from their place of origin and redeposited in water. They embrace all degrees of mixture and purity, and may be either kaolinitic or plastic.

 

Value of a Geological Survey.—On the 18th of April, 1894, the geological survey of Alabama attained its majority—twenty-one years—under the present management, with Eugene A. Smith as State Geologist. By way of memorial of the occasion maps are in course of preparation showing the condition of our knowledge of the geology of the State at the beginning and at the end of the period, 1873 to 1894; and besides these, tables showing the relative amounts of raw