IO Thinnfeldia Leaf-Bed of Roseberry Topping. 
the cuticle resists all decay and alteration almost indefinitely. 
The cellulose substance composing the middle of the leaves turns 
gradually, after the lapse of a long period of time, into a dark, 
brittle, carbonaceous substance, formed by slow oxidisation ; 
this substance when further changed, becomes like coal.* 
In most of our fossil plants from the fine grained mud- 
stones of the Yorkshire Jurassic, a change of the same kind 
has gone on; their present condition seems to depend on 
the original proportion of cuticle to softer tissue, and on the 
changes in the leaf just before or immediately after preservation. 
It would seem as though any of the Gymnosperms with their 
thick cuticles might become mummified, and in fact we get 
some interesting specimens of Ptilophyllum (sometimes called 
Williamsonia) fronds from Cloughton Wyke. In these examples 
the soft tissues must have shrivelled before being buried, for 
little but cuticle is left. On the othet hand the same type of 
leaf from Gristhorpe does not appear mummified, because the 
cuticle is too delicate to hold together the brittle carbonaceous 
matter which represents the original bulky mesophyll. In 
the Roseberry Thinnfeldias the cuticle is very thick in com- 
parison with the bulk of the inner carbonaceous matter. 
Mummified plants of this type are very infrequent outside 
Yorkshire. Specimens of the same species as those before us, 
have been found in a somewhat mummified condition in the 
Lias near Lyme Regis, and in Sutherland. Some coniferous 
remains have been discovered in the cretaceous deposits of 
Greenland, and a few come from the Rhaetic beds of Southern 
Sweden. Mummified plants are very rare in the Carboniferous 
rocks, but good examples have been found in species of Sphenop- 
teris found in the oil-shales of Scotland, and some specimens 
of exceptional interest have recently been described by Miss 
Wills (Geol. Mag., 1914), from the Midlands and North Wales. 
A few specimens have come down to us from more recent times, 
and I have seen some from the Tertiary beds near Bourne- 
mouth. 
The Roseberry examples however, stand out above all 
others because of the vast numbers of leaves which are to be 
found there, and we are justified, I believe, in saying that the 
bed is unique. 
The leaves under consideration must be referred to the 
species Thinnfeldia rhomboidalis which was founded by 
Ettingshausen on specimens from the Lias of Steierdorf in 
* An interesting example of this natural oxidation recently came to 
my notice. I received a sample of wheat from an ancient Egyptian 
granary between 5,000 and 6,000 years old. Each grain retained perfectly 
its shape and external markings, but had become converted into a dense 
black brittle substance, with a relatively high percentage of carbon, and 
reminding one very much of some of the seeds found at Gristhorpe. 
Naturalist, 
