316 Proceedings of the Royal Physical Society. 
XXII. The Origin of the Bituminoid Cement of the Caithness 
Flagstones. By J. G. Goopcnitp, H.M. Geol. Survey, 
PGos.,. 0.2.0. NEB O.U: 
(Read 20th January 1897.) 
It has long been known that the remarkable tenacity to 
which the Caithness Flagstones owe so much of their com- 
mercial value is largely due to the high percentage of 
bituminoid matter by which their constituents are cemented. 
It is this cement which enables cliffs of these rocks to 
withstand the action of the sea, which they do even in those 
cases where they are thinly bedded, and are at the same 
time traversed by well-marked joints cutting undeviatingly 
through a considerable thickness of rock. Analyses of the 
Caithness Flagstones show that some parts of these rocks 
contain as much as thirty per cent. of bituminoid matter. 
This permeates certain bands of the rock to such an extent, 
Dr Traquair tells me, that a microscopic examination of the 
organic tissues of the embedded fossils is often rendered 
next to impossible. In the field, too, the large quantity of 
bituminoid matter present causes this substance to exude 
from the rock-surfaces in a manner that reminds one of the 
resin given off from fir trees. A fact of this kind could 
hardly fail to attract attention from commercial men; and 
accordingly we find that it has more than once been seriously 
proposed to work these bituminiferous bands for the distilla- 
tion of paraffin, or even for the manufacture of gas. 
The organic origin of the substance under notice has long 
been recognised, and has probably never been called in 
question. By the great majority of geologists the source of 
the bituminoid has generally been supposed to be matter of 
animal origin—in great part due to the decomposition of the 
remains of the fossil fish which occur in these rocks. The 
object of the present note is to show that it is highly prob- 
able that substances of vegetable origin have had a large 
share in the formation of the hydrocarbon compound in 
question ; and that, in some cases, it may be due to vegetable 
matter entirely. 
