700 GEOGRAPHICAL AND GEOLOGICAL BOTANY. 



and shells, which are of a very persistent nature, and are found abundantly 

 in stratified rocks. The preservation of fossils can only have occurre'd 

 through the agency of water, impregnated with mineralizing matter, or 

 loaded with mud which enclosed the remains : the vegetable bodies which 

 can resist the long-continued action of water are few ; and these mostly 

 afford only characters of large sections of the vegetable kingdom, without 

 furnishing generic, far less specific distinctions. Added to the fragmentary 

 character of the fossils known, those kinds hitherto found possibly only 

 represent partially prevailing forms of vegetation. 



Attempts, however, have been made, by combining the conclusions of 

 stratigraphical geology and animal paleontology with those of vegetable 

 palaeontology, to form conceptions of the character of the vegetation of 

 succeeding geological periods. The ideas obtained in this way, however, 

 are very superficial and exceedingly speculative. Still there is much that 

 is promising in the investigations ; and the general tendency of all the 

 facts hitherto collected is to indicate that there has been a gradually 

 increasing complexity of organization in the plants successively created, 

 that the plants of the earliest epochs belong to the lower Classes, and that 

 the higher Phanerogams appeared only in the later formations in the last 

 of these probably in smaller proportion than in existing vegetation. In 

 the earliest formations (Cambrian, Silurian, &c.) the few vegetable 

 remains are those of Algae, Fucoids, &c. In the Devonian and Carboni- 

 ferous periods vascular Cryptogams, Ferns, Lycopods, Equiseta prevailed. 

 In the Triassic and Oolitic periods Gymnosperrnous plants formed a 

 marked feature, such as Conifers, Cycads, &c., with Tree-ferns and traces 

 of Monocotyledonous plants. With the Cretaceous period appear Angio- 

 spermous plants, beginning with a preponderance of Incomplete, and 

 passing through Dialypetalse to the more recent formations, where 

 Gamopetalous plants prevail. But in all cases, though there is evidence 

 of progress, there is an overlapping of the characteristics of one period by 

 those of another. 



One important point, however, must not be overlooked in inquiries 

 relating to this subject ; that is, the probability of the coexistence of 

 diversified local floras, as at the present day, the remains of which 

 might, from purely systematic considerations, be regarded as of different 

 antiquity. 



In illustration of this, it may be observed that the remains found in the 

 European formations belonging to the epoch immediately preceding the 

 present offer a general resemblance to the prevailing forms of existing 

 jNorth-American vegetation. 



Sect. 2. FOSSIL PLANTS CHARACTERIZING PARTICULAR 

 GEOLOGICAL FORMATIONS. 



1. Flora of the Palceozoic Strata. 



Lower and Middle Palaeozoic, or Transition Period. Comparatively 

 few plants are known in these strata, and a considerable amount of un- 

 certainty exists in reference to the determination of the fossils. What 

 remnants remain in the Cambrian, Silurian, and Lower Devonian series 

 are apparently those of marine Alga3. In the more recent deposits of this 

 age Ferns, including some allied to Hymenopliyllum and Trichomanes, 



