American Fossil Cycads. 243 
Thanks to the labours of himself, Professors Lester Ward and 
O. C. Marsh and others in America, these plants are now known 
from the Trias of Pennsylvania and N. Carolina, through the 
Jurassic of Colorado and the Potomac Formation of Maryland, to 
the Upper Jurassic, Wealden or Lower Cretaceous of the Black 
Hills of S. Dakota and Wyoming. These last localities have been 
by far the most fruitful source of the interesting material which 
forms the subject-matter of the volume before us. 
In the old world they have been found in the Gondwana 
system of India ; in England the researches of Mantell, Buckland, 
Carruthers, Williamson, and Seward have shewn how they occur 
in the Lias, Wealden and Lower Greensand. Morifere and Lienier 
described French specimens from the Middle Lias and Oolite; 
Walch, and later Ward, the specimens from Galicia; and Capellini 
and Solms-Laubach the two specimens known from Italy. At the 
conclusion of this chapter the author points out how large a part of 
the field is as yet wholly unexplored, citing the greater part of the 
Rocky Mountain Chain, the western slopes of the Andes, the 
mountain chains of Asia, &c., &c., in this connection. 
Chapter II. is devoted to a consideration of the mode of 
preservation and the external characters of these plants. It is 
interesting to note how a study of the mode of, and conditions 
attending, fossilisation 1 in the different localities is very useful for the 
comprehension of the external conformation and appearance of the 
various trunks. These are mostly bulbous, or sub-spherical in out¬ 
line and were much given to branching. Unbranched forms also 
occurred ; of these some, e.g., the Jurassic Cycadella were, like the 
modern Bowenia, small and rarely branched; others, e.g., Cycadeoidea 
gigantea and Jenneyana, were columnar and probably reached a 
height of two to three metres. 
The great diversification of trunk-form, far surpassing that of 
modern Cycads, stands out as a striking and important fact. 
Chapter III. deals with the methods of section-cutting. 
The second section of the book treats of the vegetative features 
of the Cycadeoidete, of which Chapter IV. gives a detailed 
description of the trunk-structure, including the armour, the leaf- 
bases, the cortex, the xylem zone, and the medulla. The great 
development of the woody cylinder, comparable to that of Cordailes, 
is characteristic of C. yenneyana and C. ingens. 
1 Silicification, resulting in the formation of almost perfect casts 
of the tissues, was the process concerned. 
