Fossil Wood and Lignites — Knowlton. 108 
The silicified wood occurs in situations similar to the lignite, 
but generally in larger pieces. One trunk seen by Messrs 
McGee and Ward at the new reservoir, Washington, was about 
twenty feet below the surface and was reported to have been 
between thirty and forty feet long. It had a diameter of near- 
ly two feet and was but slightly flattened. Other smaller speci- 
mens from the same locality were more flattened, and a trans- 
verse section as seen under the microscope shows the cells to be 
distorted by pressure. Generally, however, the tissue is very 
perfectly preserved in the silicified specimens and admits of 
careful dissection and study. 
In color the specimens vary from almost white to jet black, 
sometimes showing a transition between the two colors in the 
same specimen. The only examples of a decided yellow were 
collected by W. J. McGee in a cut on the Baltimore & Ohio R. 
R., half way between Montello and Reeves Station, D. C. 
These were small fragments yet they have the structure very 
perfectly preserved in places. 
The method employed in preparing these woods for study is 
that commonly followed in the preparation of petrographic 
specimens, viz: slicing and grinding to the requisite thinness 
and mounting in Canada balsam. 
SYSTEM A.TIC DESCRIPTION OF LIGKITB. 
A great many specimens of lignite have been examined by 
the process mentioned above; from Baltimore; from the new 
reservoir and vicinity, Washington; from Fort Washing- 
ton on the Potomac; from the Dutch Gap on the James river, 
and from other localities throughout the area covered by this 
formation; and the result, although not as satisfactory as could 
be wished, is probably all that could be expected under the 
circumstances. The most casual examination shows that this 
material has been subjected to great pressure, which has so en- 
tirely crushed and distorted the cellular elements that it is 
difficult in many cases to recognize the original form. The 
examination of a large series of sections serves however, to 
give a pretty correct general idea of it. A transverse section 
shows the lumen of the cells to be almost entirely closed up, 
the result of lateral pressure. This specimen, which was col- 
lected in the new reservoir, Washington, by Mr. McGee, is one 
of the Viest obtained. In most of those studied the pressure had 
