40 
Mr. William Phillips on the 
Since the grey chalk assumes a darker colour as more of the 
stratum rises to view, it seems probable that it passes into the blue 
marie by insensible degrees. There is however a great difference 
in the organic remains of these two strata ; at least in their me- 
chanical texture ; those shells which were nacreous when recent, 
rarely shew the pearly lustre in the grey chalk, while those which 
are found in certain parts of the blue marie are rarely without it : 
but this is generally the case with shells originally nacreous, which 
are found in beds of clay ; the close texture of the clay having 
protected them from the action of air and moisture. 
Among the numerous fragments of fossil wood imbedded in this 
marie, but which chiefly lie on the green sand, some are several 
inches in diameter, and still retain the woody fibre : they are mostly 
enveloped in, or the interstices of their outer part are filled with 
pyrites, which is commonly in a state of decomposition, one of the 
consequences of which is the formation of selenite in crystals, 
which are often well defined. These are either attached to the 
fossil wood, or lie imbedded near it. Some small masses of a sub- 
stance having the appearance of bone in a fossil state have been 
discovered. 
By far the greater proportion of those shells of which the nacre 
is extremely brilliant and sometimes even irridescent, are inclosed 
in more compact masses of a lighter and more uniform grey colour 
than the marie itself. On submitting 100 parts of this substance 
to the action of acid, my brother found that 3 were lost, indicating 
the presence of 7 per cent, of carbonate of lime. 
to look for them. In the course of a month or two, I however hope to send you a few 
specimens, and shall be most happy if the Geological Society should find them worth their 
acceptance. J remain, &c. 
^entlergare, Nov. 15th, 1817, 
L. W. Dillwyn. 
