LL ———— KK  & | 
OLD RED SANDSTONE OF WESTERN EUROPE. 389 
Oreadie, both over the area of Caithness and Orkney. Of Caulopteris Peachii, 
believed by SALTER to be a tree-fern, large stems have been obtained by Mr PEacu 
from South Head, Wick, and from the upper flagstones near Thurso. Pinnularia 
occurs at South Head. The most highly organised vegetation yet obtained 
from these strata are remains of coniferous wood assigned to the genus Aran- 
carioxylon. ‘The true coniferous internal structure was originally detected by 
QUECKETT, and his observations have been confirmed by Mr Peacu. No true 
marine plants have yet been found in any part of the Caithness flagstones. 
Fragments, probably of Pterygotus, certainly of some large crustacean, occur 
in the plant-bearing calmstone of Kilmster. Annelide burrows, in pairs, were 
figured by Mr Satrer as occurring at the same locality.* The small phyllopod 
crustacean, Hstheria membranacea, occurs both at Reiss and at Wick. It will 
be observed from the table, p. 451, that several of the species of fish range 
through almost the entire series of the Caithness flagstones. Dipterus macro- 
lepidotus, in particular, has the widest range of any of the Caithness fishes, for 
it occurs far down im the eastern group at Berriedale, and likewise in the beds 
of Huna, near the top of the northern or upper groups. Diéplopterus borealis, 
and Osteolepis macrolepidotus, have likewise a wide vertical range. At the 
same time, the table enables us to recognise certain positive and negative 
characters as distinguishing the two flagstone groups. Dzipterus Valenciennesit, 
and Osteolepis arenatus, which occur in great numbers at South Head, Wick, 
seem to be peculiar to the lower or Wick group ; and there may be other forms 
or varieties which do not pass upward from these strata. But according to 
present information, it is rather by the absence of many genera and species 
found in the higher groups, than by the presence of forms peculiar to itself, that 
the great group of the lower flagstones is distinguished. Thus the genera 
Acanthodes, Diplacanthus, and Parexus, found in the Forfarshire flagstones, 
have only been noticed in Caithness from the Thurso group. The Osteolepis 
microlepidotus, so characteristic of that group, has not been observed in the 
Wick flagstones. The range of Coccosteus pusillus is equally restricted. The 
land plants, also, in the lower group are neither individually nor generically so 
numerous as they become higher in the series. How far these paleontological 
| distinctions are radical, depending upon the chronological sequence of the 
organic forms, or accidental, arising from original conditions of hydrography 
and deposit, it would be premature at present to decide. I believe, however, 
and will be able to show in a later part of this memoir, that they probably do 
point to chronological sequence, and may therefore be used to some extent as 
a means of making out the stratigraphical relations of the Old Red Sandstone 
of the north of Scotland. 
* “Quart. Journ. Geol. Soc.” vol. xiv. p. 72, and plate v. fig. 6. 
VOL. XXVIII. PART II. oI 
