Ch. XVII] AT AIX-LA-CHAPELLE. 333 



pated, are very rarely met with. In the neighborhood of Aix-la-Cha- 

 pelle, however, an important exception occurs, for there certain white 

 sands, 400 feet in thickness, contain the remains of terrestrial plants 

 in a beautiful state of preservation. These have been diligently col- 

 lected and studied by Dr. Debey, and as they afford the only example 

 yet known of a terrestrial flora older than the Eocene, in which the 

 great divisions of the vegetable kingdom are represented in nearly the 

 same proportions as in our own times, they deserve particular atten- 

 tion. Dr. Debey estimates the number of species as amounting to 

 more than two hundred, of which sixty-seven are cryptogamous, 

 chiefly ferns, tweuty species of which can be well determined, most 

 of them being in fructification. . The cicatrices on the bark of one or 

 two are supposed to indicate tree-ferns. Of thirteen genera three are 

 still existing, namely, Gleichenia, now inhabiting the Cape of Good 

 Hope and New Holland ; Lygodium, now living in Japan, Java, and 

 North America ; and Asplenium, a cosmopolite form. Among the 

 phsenogamous plants the Conifers are abundant, the most common be- 

 longing to a genus called Cycadopteris by Debey, and hardly separable 

 from Sequoia (or Wellingtonia), of which both the cones and branches 

 are preserved. When I visited Aix, I found the silicified wood of this 

 plant very plentifully dispersed through the white sands in the pits 

 near that city. In one silicified trunk 200 rings of annual growth had 

 been counted. Species of Araucaria like those of Australia are also 

 found. Cycads are extremely rare, and of Monocotyledons there are 

 but few. No palms have been recognized with certainty, but the genus 

 Pandanus, or screw pine, has been distinctly made out. The number 

 of the Dicotyledonous Angiosperms is the most striking feature in so 

 ancient a flora. * 



Among them we find the familiar forms of the Oak, Fig, and Wal- 

 nut, Quercics, Ficus, and Juglans, of the latter both the nuts and leaves ; 

 also several genera of the Myrtaceoe. But the predominant order is 



* In this and subsequent remarks on fossil plants I shall often use Dr. Lindley's 

 terms, as most familiar in this country ; but as those of M. A. Brongniart are 

 much cited, it may be useful to geologists to give a table explaining the corre- 

 sponding names of groups so much spoken of in palaeontology. 



Brongniart. Lindley. 



•| } 1. Cryptogamous araphi- 



I J gens, or cellular \ Thallogens. Lichens, sea-weeds, fungi. 



cryptogamic. 

 Cryptogamous aero- Acrogens. Mosses, equisetums, ferns, lyco- 



gens. podiums, — Lepidodendron. 



Dicotyledonous gym- Gymnogens. Conifers and Cycads. 



nosperms. 

 Dicot. Angiosperms. Exogens. Composite, leguminosse, urn- 



belliferre, crucrfcrge, heaths, 

 I 1 &c. All native European 



trees except conifers. 

 5. Monocotyledons. Endogens. Palms, lilies, aloes, rushes, 



grasses, &c. 



