232 ANNUAL OF SCIENTIFIC DISCOVERY. 



it. Plants must therefore have preceded animals upon the globe 

 and spontaneous generation, if it were possible, should result iii 

 the production of plants first, of animals only from them, 11'.'- 

 mains of plants occur in the oldest rocks, but only of the lowest 

 types, seaweeds. 



The first land plants appear in the upper devonian rocks, coni- 

 fers, ferns, lycopods, etc., the advance guard of the carbonifer- 

 ous flora, and having the same general character. From the 

 variety and comparatively high organization of these plants \ve 

 must infer either the somewhat sudden creation of an elaborate 

 flora, or a great hiatus in geological history, in which its origin 

 and development are lost. 



The carboniferous flora of America is essentially the same as 

 that of the coal measures of the Old World. Of 600 species recog- 

 nized here, at least one-third are considered identical with Euro- 

 pean forms, while the genera are nearly all the same. 



The carboniferous period was one of depression in this country, 

 the western part of the continent being all beneath the ocean, 

 though extensive land-surfaces had existed there before. A belt 

 of country north of the St. Lawrence was then as it has con- 

 stantly been since the beginning of the palaeozoic ages out of 

 water, as was most of New York, and part of New England. 

 The coal-plants grew in marshes on the western margin of the 

 land, at the sea level; a gradual submergence producing a suc- 

 cession of vegetable deposits, one above another. The climate 

 was moist, uniform, and warm, but not hot, as vegetable matter 

 would, in that case, have decayed and not bitumenized. The at- 

 mosphere was also more highly carbonated than now. From the 

 similarity of the flora of the coal measures in different countries 

 we must conclude that all the vegetation of the world at this pe- 

 riod was of the character indicated by these specimens, and that 

 more highly organized plants had not yet been called into exist- 



o 



ence. 



The permian flora was not represented in any collection made 

 on this continent ; but from the plants obtained from the permian 

 rocks abroad, it was evident that the flora of that period was, like 

 the fauna, but a continuation of that of the carboniferous. 



In passing the interval which separates the mesozoic from the 

 palaeozoic ages we enter a new world, in which all the aspects of 

 nature were quite unlike those of the preceding periods. New 

 molluscs and new fishes swam in the seas ; reptiles were the 

 monarchs of animated nature, swimming, walking, flying, car- 

 nivorous and herbivorous, in size ranging from the mouse to the 

 whale, they filled the places now occupied by reptiles, birds, and 

 mammals. The vegetation of the triassic and Jurassic periods was 

 as peculiar as the fauna, and constituted a distinct chapter in the 

 botanical history of the world. The most conspicuous plants of 

 this flora were the cycads, which had no existence before, and 

 have since formed but an insignificant portion of the vegetation 

 of the earth's surface. 



With the commencement of the cretaceous period the flora of 

 the world was again revolutionized, and the highest order of 



