THE EARLIEST PLANTS. 795 



carbonaceous debris, Avhich seems to be the remains of either aquatic 

 or land plants, is locally not infrequent. 



Referring to the land vegetation of the ojder 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 Protan- 

 nularia and some tall trees, perhaps looking like gigantic club-mosses, 

 or possibly with broad, flabby leaves, mostly cellular in texture, and 

 resembling algaj transferred to the air. Imagination can, however, 

 scarcel}^ realize this strange and grotesque vegetation, which, though 

 possibly copious and luxuriant, must have been simple and monoto- 

 nous 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 garment? 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 submei'gence 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. 

 AVe may write of them and draw their forms with the carbon which 

 they themselves supplied. 



The 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 in- 

 habitants who were 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 imequal to the 

 strain of metropolitan life. The death-rate of young women is low, partly be- 

 cause 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. 



