82 THE STORY OP THE EARTH AND MAN. 



stone spreads more widely than that of the Upper 

 Silurian, and in no previous period have we much less 

 evidence of the existence of dry land ; yet before the 

 end of the period we observe, in a few fragments 

 of land plants scattered here and there in the marine 

 limestones evidence that islands rose amid the waste 

 of waters. As it is said that the sailors of Columbus 

 saw the first indications of the still unseen Western 

 Continent in drift canes, and fragments of trees float- 

 ing in mid ocean, so the voyager through the Silurian 

 seas finds his approach to the verdant shores of the 

 Devonian presaged by a few drift plants borne from 

 shores yet below the horizon. The small remains 

 of land in the Upper Silurian were apparently limited 

 to certain clusters of islands in the north-eastern part 

 of America and north-western part of Europe, with 

 perhaps some in the intervening Atlantic On these 

 limited surfaces grew the first land plants certainly 

 known to us herbs and trees allied to the modern 

 club- mosses, and perhaps forests of trees allied to the 

 pines, though of humbler type ; and this wide Upper 

 Silurian sea, with archipelagos of wooded islands, may 

 have continued for a long time. But with the begin- 

 ning of the Devonian, indications of an unstable 

 condition of the earth's crust began to develop them- 

 selves. New lands were upheaved; great shallow, 

 muddy, and sandy flats were deposited around them ; 

 the domains of corals and sea- weeds were contracted ; 

 and on banks, and in shallows and estuaries, there 

 swarmed shoals of fishes of many species, and some of 



