FIRST PERIOD OF THE ANCIENT WORLD. 11 
stone, although so striking in its mineralogical appearance, is, however, by 
recent examination, proved to be a member of the mountain limestone. 
The account of a large fossil tree which was exposed in the lower part 
of Craigleith Quarry, near Edinburgh, in 1826, will more properly be given 
in the Third Section, as I have presented the appearances which its or- 
ganic texture exhibits under the microscope. The height of this gigantic 
plant was 36 feet, its diameter at the base 3 feet. It lay nearly in a hori- 
zontal position, parallel to the stratification of the sandstone in which it was 
imbedded. It will be seen, from the structure of this tree, that it is ap- 
parently referrible to the Conifer. This plant, therefore, as well as others 
of which I shall take particular notice, forms an exception to the supposed 
general distribution of the primitive vegetation. 
Thus, in these great coal-fields, we find the opinion of M. A. Brone- 
NIART most completely verified, namely, that the vascular cryptogamic 
plants had a vast preponderance in their numerical proportion ; and, in fact, 
of 260 species discovered in this terrain or period, 220 belong to that class. 
* Should, however,” adds M. BRoNGNIART, “ more precise observation, 
or new discoveries, make known in the old formation some plants of more 
than one of the classes which we have admitted, or even some species of one 
of the classes which have appeared to us to be wanting at this epoch, still 
the essential relations of these classes to each other, would be but slightly 
modified. Thus, it might be proved that certain, yet little known genera 
of the coal-formation are true dicotyledonous plants, yet it would not be the 
less certain, that the vascular cryptogamic plants were by much the most 
numerous vegetables during the first period of vegetation.” The same re- 
marks he makes respecting the lias, and other formations. Thus, what- 
ever discoveries may be made among the vegetables of this period, from 
the first deposit of the transition rocks to the top of the coal-field, yet the 
essential characters can be but slightly modified, and this period will always 
remain distinct. Notwithstanding these remarks, I think we have reason 
to believe, from the great numbers of Conifer found in the mountain lime- 
stone group of Berwickshire, that a much greater proportion of these plants 
B2 
