191 
TAB. CCXCVI. 
FERRUM oxygenizatum argillaceum. 
Argillaceous Iron-Stone. 
Class 3. Metals. Order 2. Mixed. 
Gen. Ferrum oxygenizatum. Spec. Argillaceum. 
Div. 1. Amorphous, 
See ee ee a 
Tron-stones with vegetable impressions, or rather exuviz, 
have been much noticed by many writers, but have scarcely 
been admitted into mineralogical works: we should, there- 
fore, be at a loss in most instances to find an account of 
them, where we would wish to see them spoken of as a part 
of the great system, especially of the phanomena of the 
change, or seeming conversion, of one substance into an- 
other. How bits of ferns or such plants should become so 
regularly immersed in the clayey Iron-Stone balls upon the 
Coal strata as they are found to be, can only be guessed at. 
They not only contain a certain portion of the plant, but 
often so regular a fragment that it would hardly be possible 
to put a more complete fragment between two pieces of 
clay, and press them into a ball, more or less ovate, as 
these generally are. Were I to endeavour to account for 
this appearance, I should suppose the plants to have been 
formerly in or near ferruginous loamy or clayey soil ; that 
their tops being much shaken as by a watery or showery 
tempest, were continually heating against the unctuous 
clayey cliff, and thereby became loaded with clay, till the 
branch was detached by help of its cumbrous load; and 
being at length covered by the deluged soil, has remained 
to this time, a lasting memorial of a catastrophe of which 
we can only expect to see such signs, although it seems to 
say we are indebted to it for the Coal formation, which I 
think is more confirmed in these instances. The peculiar 
change here wrought is an excellent specimen to show us 
that, under these particular circumstances, all vegetables 
