262 HISTORICAL PALEONTOLOGY. 



been found chiefly in certain sands in the neighbourhood of Aix- 

 la-Chapelle, and they consist of numerous Ferns, Conifers (such 

 as Cycadopteris\ Screw Pines (Pandanus), Oaks ( Quercus), Wal- 

 nut (Juglans), Fig (Ficus], and many Proteacea, some of which are 

 referred to existing genera (Dryandra, Banksia, Grevillea, &c. ) 



In North America, the Cretaceous strata of New Jersey, 

 Alabama, Nebraska, Kansas, &c., have yielded the remains of 

 numerous plants, many of which belong to existing genera. 

 Amongst these may be mentioned Tulip-trees (Liriodendron), 

 Sassafras (fig. 186), Oaks (Quercus), Beeches (Fagus), Plane- 

 trees (Platanus), Alders (Alnus}, Dog-wood (Cormis), Willows 

 (Salix), Poplars (Populus), Cypresses (Cupressus), Bald Cy- 

 presses (Taxodiuni), Magnolias, &c. Besides these, however, 

 there occur other forms which have now entirely disappeared 

 from North America as, for example, species of Cinnamomum 

 and Araucaria. 



It follows from the above, that the Lower and Upper Creta- 

 ceous rocks are, from a botanical point of view, sharply sepa- 

 rated from one another. The Palaeozoic period, as we have 

 seen, is characterised by the prevalance of " Flowerless" plants 

 (Cryptogams), its higher vegetation consisting almost exclu- 

 sively of Conifers. The Mesozoic period, as a whole, is charac- 

 terised by the prevalence of the Cryptogamic group of the 

 Ferns, and the Gymnospermic groups of the Conifers and the 

 Cyca.ds. Up to the close of the Lower Cretaceous, no Angio- 

 spermous Exogens are certainly known to have existed, and 

 Monocotyledonous plants or Endogens are very poorly repre- 

 sented. With the Upper Cretaceous, however, a new era of 

 plant-life, of which our present is but the culmination, com- 

 menced, with a great and apparently sudden development of new 

 forms. In place of the Ferns, Cycads, and Conifers of the earlier 

 Mesozoic deposits, we have now an astonishingly large number 

 of true Angiospermous Exogens, many of them belonging to 

 existing types ; and along with these are various Monocotyle- 

 donous plants, including the first examples of the great and im- 



' 'cotyledon." Hence these plants are often simply called "Monocotyledons." 

 The Exogens, on the other hand, have a true bark ; and the stem increases 

 by annual additions to the outside, so that rings of growth are produced. 

 The young plant has two seed-leaves or "cotyledons," and these plants 

 are therefore called il Dicotyledons." Amongst the Exogens, the Pines 

 (Conifers) and the Cycads have seeds which are unprotected by a seed- 

 vessel, and they are therefore called " Gymnospenns." All the other 

 Exogens, including the ordinary trees, shrubs, and flowering plants, have 

 the seeds enclosed in a seed-vessel, and are therefore called " Angio- 

 sperms." The derivation of these terms will be found in the Glossary at 

 the end of the volume. 



