Page:Popular Science Monthly Volume 32.djvu/817

Rh carbonaceous débris, which seems to be the remains of either aquatic or land plants, is locally not infrequent.

Referring to the land vegetation of the older rocks, it is difficult to picture its nature and appearance. We may imagine the shallow waters filled with aquatic or amphibious rhizocarpean plants, vast meadows or brakes of the delicate Psilophyton and the starry Protannularia and some tall trees, perhaps looking like gigantic club-mosses, or possibly with broad, flabby leaves, mostly cellular in texture, and resembling algæ transferred to the air. Imagination can, however, scarcely realize this strange and grotesque vegetation, which, though possibly copious and luxuriant, must have been simple and monotonous in aspect, and, though it must have produced spores and seeds and even fruits, these were probably all of the types seen in the modern acrogens and gymnosperms.

 In garments green, indistinct in the twilight, They stand like Druids of old, with voices sad and prophetic."

Prophetic they truly were of the more varied forests of succeeding times, and they may also help us to realize the aspect of that still older vegetation, which is fossilized in the Laurentian graphite; though it is not impossible that this last may have been of higher and more varied types, and that the Cambrian and Silurian may have been times of depression in the vegetable world, as they certainly were in the submergence of much of the land.

These primeval woods served at least to clothe the nakedness of the new-born land, and they may have sheltered and nourished forms of land-life still unknown to us, as we find as yet only a few insects and scorpions in the Silurian. They possibly also served to abstract from the atmosphere some portion of its superabundant carbonic acid harmful to animal life, and they stored up supplies of graphite, of petroleum, and of illuminating gas, useful to man at the present day. We may write of them and draw their forms with the carbon which they themselves supplied.

considerations adduced by Professor Alfred Marshall, in answer to the question whether London is healthy, are applicable to other large cities. Many people live long in the metropolis, not because it is healthy, but because their exceptional health and strength induced them to come there. Most of the inhabitants who wore born elsewhere were, when they came, the picked lives, the strongest members of their several parishes. Numbers of London-born people have gone away to live elsewhere because they felt themselves unequal to the strain of metropolitan life. The death-rate of young women is low, partly because of the favorable conditions of life of domestic servants, and partly because young people who come to the city are likely to go home as soon as they get ill, to swell, perhaps, the death-rate of their native towns. Really, London is very unhealthy; for, although the population consists mainly of picked lives, and despite all the resources of wealth to counteract disease, the expectation of life is below the average.