7 
THE THINNFELDIA LEAF-BED OF ROSEBERRY 
TOPPING. 
H. HAMSHAW THOMAS, M.A., F.G.S., 
Fellow of Downing College, Cambridge, 
THE locality of Roseberry Topping is well-known to all York- 
shire geologists, and many will have studied personally the 
fine exposure of Lower Estuarine deposits laid bare by the slip 
on the north-west side. On one of my early visits to this 
exposure, I discovered fragments of a thin bed which seemed 
to be composed very largely of fragments and leaflets of the 
fronds which are known under the generic name of Thinnfeldia. 
At that time the fall of material from the face above was 
going on almost continuously, and it was scarcely safe to 
venture far in quest of more of these specimens, but in the 
following year, when the ground was becoming settled, I 
obtained further examples which demonstrated the abundance 
of these leaves at a certain level in the dark-coloured lower beds 
lying above the Lias. In the spring of 1913 I set out to try 
to trace the plant beds from Roseberry Toppirg across to the 
main escarpment, known, I believe, as Little Roseberry, and 
here encountered in a scrape on the hill side, the main portion 
of the Thinnfeldia leaf-bed, which is undoubtedly one of the 
most remarkable fossil-plant deposits in Europe. I subse- 
eemtly excavated this bed, and have made large exposures 
at two places about a hundred yards apart, an from here 
the specimens exhibited* were obtained. 
We have in these exposures a thickness of 8 to 10 feet of 
black or dark chocolate shales containing throughout an abund- 
ance of leaves which are almost all of the same species. In 
many places the leaves are so numerous that in a thickness of 
several inches the bulk of the bed is composed of leaves with 
comparatively little sediment round them. I have not yet 
succeeded in determining any definite periodicity in the succes- 
sive layers, but there are some indications that the leaves were 
not deposited uniformly. The beds at Little Roseberry seem 
to rest directly upon the gray shales of the Upper Lias, and 
seem quite conformable with them so far as can be made out. 
There is no indication of anything comparable to the ferru- 
ginous dogger of Whitby. The massive sandstone which forms 
such a conspicuous feature in the neighbourhcod, is many feet 
above at this point. 
At Roseberry Topping I noted the following sequence at 
the top of the Lias on the east side of the slip :— 
Black Shales with sandy partings 
Thinnfeldia and other forms at their base | See 
* These have been kindly presented to the Museum at Hull.—Ep. 
1915 Jan. 1. 
