Fossil Wood and Lignites — Know!,ton. 105 
silicilied examples, it is probable that most of the lignite may 
be aho of this genus, particularly as there is in many cases a 
marked resemblance, so far as I am able to interpret the dis¬ 
torted structure, between it and some of the species described 
from silicified specimens. Also several species probably entered 
into the composition of this lignite. 
SYSTEMATIC RELATIONS OF THE SILICIFIED MATERIAL. 
As I have before stated the cellular elements are much better 
preserved in the silicified examples than in the lignite, and the 
results are more reliable and satisfactory. The tissues are here 
preserved with little if any alteration in shape and retain all 
their markings in the highest state of perfection. 
This silicilied material is all coniferous. It belongs to two 
well known genera, Cupressinoxylon with four species and 
ArauCarioxylon with a single species. 
Cupressinoxylon. This genus as now understood has a 
somewhat comprehensive meaning, and includes according to 
Kraus what were at one time regarded as several distinct 
genera. Thus we have Thuioxylon of Unger and Endlicher; 
Fhysematopitys of Goppert; a part of Pinites of Goppert and 
Pence of Witham all embraced under the genus Cupressinoxy¬ 
lon. It is the largest genus known in which the species are 
founded entirely upon internal structure, and it has represen¬ 
tatives from the Carboniferous to the Tertiary. This genus is 
thought by eminent authorities, such as Goppert, Mercklin and 
Schmalhausen, to represent the wood of Sequoia, since the des¬ 
cribed species have a great structural resemblance to the living 
species of Sequoia, and moreover are usually found associated 
in the fossil state with leaf and cone impressions that undoubt¬ 
edly belong to Sequoia. This view is strikingly confirmed in 
the present instance as Prof. Fontaine has described from leaf 
and cone impressions no less than twelve species of Sequoia 
from the Potomac flora, and typical cones have been found at 
Beltsville, Maryland, associated with the lignites and silicified 
wood. The individuals belonging to this genus must have 
been exceedingly numerous during the reign of the Potomac 
flora as their abundant remains testify. It is altogether 
probable that some of the species 1 have described from in¬ 
ternal structure may represent the'wood of some of those 
