36 MR STEVENSON ON THE GEOLOGY OF COCKBURNLAW, 
plainly marked, and the plates of a different shape and style of sculpture, being 7e- 
ticulated instead of tuberculated. The teeth are beautifully fluted, and appear 
to belong to the Dendrodus striatus of Professor OweEn, to which fish the asso- 
ciated scales, plates, and spines probably also pertained. 
In Prestonhaugh there are found, besides the remains of the Holoptychius, 
other relics of a more obscure and puzzling, but highly interesting character, and 
seem to be of organic origin, though all trace of their original organic matter has 
which disappeared. These present many varieties of size and form, the most com- 
mon being spindle-shaped bodies, which project in relief from the surfaces of the 
strata in which they occur. These are generally about halfan inch long, detached, or 
connected by threadlike ridges. Another sort resembles in form and size the cry- 
salis of a butterfly, while others present a vermiform appearance. It seems pro- 
bable that the majority of these curious markings are nothing else than the petri- 
fied forms of soft-bodied animals that crawled in the mud of those ancient shores, 
and which, being covered by a deposit of sand, left the outline of their forms im- 
pressed thereon, the gases evolved in the process of decomposition escaping through 
the sand, and being replaced by the infiltration of the finer particles of mud. 
Others are perhaps coprolitic, and some, probably, mere concretions. ‘The appear- 
ances presented by the bottom of a shallow pool which has been recently dried 
up, afford an apt illustration of some of these markings, the smooth glazed surface 
of the mud being marked here and there with worm-pits and castings, and furrowed 
by the traces of worms and insects, while it is divided into irregular portions by 
fissures of desiccation. In fact, some of these recent markings are almost perfect 
fac-similes of those which occur among the rippled strata of Prestonhaugh. Nor 
is evidence awanting among these strata of fissures having been produced by desic- 
cation. ‘There is one bed, in particular, of whitish sandstone, overlying strata of a 
softer and more clayey character, the under surface of which, wherever exposed, 
is seen to be entirely covered with relieved mouldings, which ramify in all direc- 
tions, forming a sort of irregular net-work, and in short, exactly resembling the 
appearance which would be presented by the under surface of any plastic or mol- 
ten substance poured into the cracks produced in mud by the heat of the sun. 
The depressions between these reticulated mouldings are generally smooth and 
shining, being coated with a fine red clay. Scales of the Holoptychius also occur 
pretty frequently on the same surface. 
These interesting strata are succeeded by others in which the clays rather 
predominate, and which seem to be quite destitute of organic remains. They are, 
however, profusely marked with greenish-white spherical spots, of various sizes, 
from that of a pea, up to several inches in diameter. The colouring matter of the 
sandstone (the peroxide of iron) appears to have been discharged by some power- 
ful deoxidising process, probably the putrefaction of animal or vegetable matter. 
Scales of the Holoptychius are sometimes met with, surrounded by a blanched 
