Fossil Wood and Lignites — Knoirlfon. 105 
^ilicitied examples, it is probable that most of the lignite may 
be al-^o 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, lietween it and some of the species described 
from silicified specimens. Also several species probably entered 
into the composition of this lignite . 
SYSTEMATIC IiE].ATI0N8 OF THE SILICIFIKD 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 perfectioii. 
This silicitied material is all coniferous. It belongs to two 
well known genera, Cupressinoxylon with four species and 
Araucarioxylon with a single species. 
CuPKESSiNOX YLON. This genus as now understood lias 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 Eudlicher; 
Physematopitys 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 tlie 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 ussociated 
in the fossil state with leaf an<l 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 impres.sions 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 I have described from in- 
ternal structui-e may represent the wood of some of those 
