55 
also very evident that these denuding agents have like- 
wise been instrumental in removing large quantities of ore 
previously deposited, and the outliers of limestone capping 
isolated prominences in this neighbourhood, testify to the 
great extent of denudation which we may reasonably 
suppose took place at the period indicated by the eroded 
surface of the Aldby limestone. 
Mr. C. Bailey, in a letter addressed to Mr. Brockbank, 
states that the chief portion of the vegetation referred to in 
the preceding paper consists of dark-coloured fragments of 
the stems of a dicotyledonous plant which seem to have 
been broken sharply off while growing in situ. They have 
the general appearance of rotten sticks, and in their fresh 
condition are very soft and friable, yielding readily to the 
knife, but with exposure to the air they dry and become 
much harder. They appear to have belonged to a shrubby 
plant of no great size, the stems of which would range be- 
tween half and three quarters of an inch in diameter. The 
internal portion of the stems has almost entirely disappeared, 
and in the few fragments examined, there are no traces of 
any woody layers, medullary rays, or central pith. The 
portions preserved consist of true bark, which is made up 
of two layers : — an exterior layer, or periderm, which is in 
a good state of preservation ; and an interior fibrous portion, 
or liber, made up of short rectangular cells, which form 
layers of considerable thickness. 
All the woody fragments examined belonged to aerial 
portions of the plant, but there are no remains of the 
leaves borne by these stems, and it would be very desirable 
that they should be sought for in the lower portion of the 
