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minute coin-like bodies which are very abundant in some coals, and which had been previously noticed by Witham, Dawson, and others. The larger of these bodies Huxley regarded as spore-cases, and the smaller as spores, while he considered that their disintegration had led in most cases to the formation of the bulk of what we call coal.

Prof. Williamson showed in detail that these were not spore-cases, but two kinds of spores—microspores and macrospores—such as severally occur in the upper and lower portions of the fruits of many living club-mosses. Their sizes and structure demonstrate the truth of this conclusion, which is further sustained by the fact that spore-cases are not deciduous, but spores are; and these objects, having fallen in such vast myriads from gigantic club-mosses, can only have been deciduous organs. The lecturer then gave reasons for concluding that these spores had played a much more limited part in the origin of coal than Huxley had assigned to them. According to Huxley, coal is composed of mineral charcoal and coal proper—the latter term being equivalent to spores altered or unaltered. Prof. Williamson, on the other hand, recognized three such elements: mineral charcoal, that is, fragments of fossil wood retaining its structure; coal proper, that is, mineral charcoal disorganized; and spores in various states.

We now distinguish in coal three groups of fossil plants: 1. Those of which we have the form but not the organization: 2. Those of which we have both form and organization; 3. Those of which we know the structure, but are ignorant of the outward form. What has yet to be done is the correlation of the first and last of these three groups. Brogniart long ago showed that most of the coal-plants were cryptogamic—chiefly calamites (allied to living horse-tails); lepidodendra (represented by the club-mosses); ferns, and plants supposed to represent pines and firs of the group known as gymnospermous exogens.

Leached Ashes as a Fertilizer.—In a report to the Connecticut State Board of Agriculture, Prof. S. W. Johnson gives the results of some analyses made by himself of specimens of leached ashes used for fertilizing purposes. By these analyses leached ashes are found to contain: less than one per cent, of potash; a large proportion of water (not less than 35 per cent.); considerable sand or soil, and unburned coal, amounting to from 6 to 15 per cent., when not intentionally or largely adulterated; about 45 per cent, carbonate of lime, which is the chief fertilizing element in leached ashes; a little more than 1 per cent, of phosphoric acid, and 3 to 4 per cent, of magnesia. They contain no nitrates, but the carbonate of lime in them favors the development of nitrates when they are incorporated with the soil, especially in conjunction with animal manures.

Prof. Johnson states that the price of this material is 35 cents per 100 lbs., or $7.00 per ton. Its fertilizing value lies exclusively in the 20 or 30 lbs. of lime, 312 of magnesia, 112 of phosphoric acid, and 1 or 2 lbs. of potash in each 100 lbs. But these materials may be procured in other forms, as follows: 35 lbs. of fresh-burned oyster-shell, or stone-lime, will furnish the lime; 15 lbs. of any good superphosphate will supply the phosphoric acid; the magnesia and potash together may be obtained in 40 lbs. of German potash salts, and there will then be 4 or 5 lbs. of potash and 6 lbs. of sulphuric acid extra.

If the lime be slaked with water in which the superphosphate and potash salts have been soaked and partially dissolved, the resulting mass will contain not only all the fertilizing elements of 100 lbs. of leached ashes and more, but these elements will be in such a state of fine division as to render the mixture in all respects equal to the ashes themselves.

From these data any one can readily calculate the cost in his own locality of a substitute for leached ashes. "It must not be forgotten," adds Prof. Johnson, "that a mixture made of fresh-burned lime should be allowed to become mild by exposure to the air, or its peculiar effects on the soil should be anticipated and provided for."

Age of Metamorphic Rocks.—"The Metamorphism of Rocks" is the title of a paper read at the Association meeting, by Prof. T. Sterry Hunt. The author briefly noticed the changes produced in rocks by