Fossil Wood and Lignites — Knowlton. 
101 
after which there was a gradual uplifting of the land. This 
newty emerged land was now subjected to the powerful action 
of moving water which cut down and transported a large por¬ 
tion of it, leaving now and then these irregular or lenticular 
masses intact which were eventually surrounded and covered by 
a lighter material and the whole was finally buried under the 
Tertiary. 
Good exposures of this formation, containing lignite and 
silicified wood, occur at Fort Washington, White House Land¬ 
ing and Acquia Creek on the Potomac; at Dutch Gap and vicinity 
on the Janies river; and also in the cities of Washington and 
Baltimore where excavations have been made. Cuts along the 
lines of rail-ways which pass through this formation often give 
good sections. Most of the material upon which the following 
observations are based, came from these localities. 
The wood of this formation occurs under two widely different 
conditions, viz: as lignite and as silicified wood. There seems 
to be almost no transition between the two forms, although in 
one instance, in a silicified specimen from the new reservoir, 
Washington, a few small lignitized areas were detected. There 
is reason for supposing, however, that some of the silicified 
forms are also represented in a lignitized state; that is, owing 
to different conditions of fossilization some specimens of a 
species were silicified, while others were turned to lignite. 
The lignite is much more abundant than the silicified form, 
occurring in the above mentioned lenticular masses in pieces of 
considerable size and in the loose surrounding material as 
minute fragments, which shows that this latter is the result of 
the wearing away of a large part of the original deposit. One 
of the largest specimens noted was found at Fort Washington. 
This was a log about five feet in length, eight inches in width, 
and four in thickness. A cross section of this specimen, of 
course, would have been lenticular, showing that it had been 
subjected to great horizontal pressure. A transverse section as 
seen under the microscope shows the cells completely collapsed 
and distorted by the pressure. 
In color this lignite is almost uniformly jet black, in only a 
few cases being of a slightly brownish cast. It has a specific 
gravity of about 1.B33, and breaks with a true conchoidai frac¬ 
ture like ordinary anthracite. When thus broken it does not 
