THROUGH THE LOWER AND UPPER STRATA. 



27 



their number or complexity, vascular plants may be divided 

 into the following classes, and each class contains distinct fam- 

 ilies : — 



1. Without perfect flowers, the organs of fructification concealed 

 (cryptogamia). To this class belong, in the fossil state, gigan- 

 tic ferns, equisetum [horse tail), and other plants allied to ferns. 



2. With flowers, tlie seeds naked or without capsules. To this 

 class belong the families cycadese and conifercB, or firs. This 

 class is denominated phanerogamia gymnospermous, 



3. Flowering plants with one cotyledon : phanerogamia mono- 

 cotyledonous. It comprises water-lilies, palms, lilies, and canes. 



4. Flowering plants with two cotyledons ; this comprises all forest 

 trees and shrubs : Phanerogamia dicotyledonous. 



None of the families of plants but those in the last class have the 

 true woody structure, or produce perfect wood, except the coniferae 

 or firs, hCf ; but the wood of these differs from true dicotyledonous 

 wood. 



In tracing tde distribution of vegetables through the different class- 

 es of rock, we shall find only the lowest or simplest forms of organi- 

 zation, in the most ancient formation. 



1. Transition slate contains, occasionally, impressions of algse or 

 sea weed ; but, considering the frail texture of the cellular 

 plants, we cannot expect the forms to be well or abundantly 

 preserved in rocks, which have probably been subjected to heat 

 and various disturbing agents. A few fronds or leaves of ferns 

 have been found in some rocks of this class. 



2. Coal-measures abound in vegetable remains of the first or low- 

 est class of vascular plants. Gigantic ferns, large equisetums 

 (horse tail), and lycopodia are of frequent occurrence. Palms 

 and canes are more rare. 



3. The secondary strata are, principally, marine formations ; but 

 the beds of sandstone and clay frequently contain vegetable 

 remains of plants of the second class (ferns and lycopodia, Sic), 

 but of different species to those found in the regular coal meas- 

 ures. In part of this series, occur fossil remains of the third 

 class, coniferae and cycadese. In the marine strata, are occasion- 

 ally found broken fossil stems, but the vegetable fossil remains, 

 appropriate to them, are of algse or sea weed. Plants of the 

 fourth class sometimes occur in the upper secondary strata. 



4^ Tertiary strata contain fossil plants of the more perfect classes, 

 which are rarely, if ever, found in the secondary strata. Some 

 of the most recent tertiary beds contain remains of trees analo- 

 gous to what now flourish in Europe. 

 The above brief outline may be taken, as a near approximation, to 

 the distribution of the different classes of fossil vegetables. The 

 instances of trees or plants of the highest class found in coal are 

 doubtful ; for stems of large lycopodia, divided into two branches 



