‘ez 
OLD RED SANDSTONE OF WESTERN EUROPE. 435: 
the lowest bed is a very calcareous breccia, in part a cornstone. Owing to the 
low angle of dip, and the coincidence between the strike of the strata and the 
trend of the coast-line, only a very limited thickness of beds can be seen between 
Buckie and the mouth of the Tynet Burn. The coast, in fact, is fringed with a 
mere strip of nearly flat Old Red Sandstone, only about a quarter of a mile 
broad. At Portgordon the thin red flagstones pass under a sandy beach, 
which, with two wonderfully well-preserved raised beaches, runs westwards 
along the shore towards the Spey. In the Burn of Tynet, however, a good 
and tolerably continuous section is afforded, one portion of which has long 
been known from the beautiful ichthyolites originally obtained from it by Dr 
MALCOLMSON. 
The total thickness of strata exposed in that section probably falls short of 
400 feet. The upper portion, perhaps 150 feet thick, consists of soft red sand- 
stones, with occasional bands of conglomerate, and of greyish-purple clay with 
calcareous nodules. These beds are underlaid by a conglomerate, which, though 
finer in its upper part, passes downward into a coarse mass, with well-rounded 
pebbles. As several faults traverse this part of the section, the true thickness 
of this conglomerate can only be inferred. Probably it is not less than 130 feet. 
On the south side of one of these faults the conglomerate is replaced by pur- 
plish-grey, red, and greenish shaly sandstone, and sandy shale with calcareous 
nodules, which occur chiefly in the grey shales or clays, but also in the red 
bands. The lower or more shaly part of this zone is about 50 or 60 feet thick. 
It is here that the fish-bearing nodules chiefly occur. Beneath the shales fine 
conglomerate crops out, and continues up the stream, until the section is obscured 
towards Tynet Bridge by overlying drifts. But the crystalline rocks appear a 
short way further up.* 
It is evident from the facts now stated, that here again, as at Gamrie, the 
ichthyolite beds occur in the heart of a thick mass of conglomerate. The 
* Since my description of the Old Red Sandstone of these northern regions was written, the work 
of the Geological Survey has commenced in that area. Mr J. G. Wrirson, who has been intrusted with 
the mapping of the district above referred to, has made the interesting discovery of a bed of diabase- 
porphyrite, interstratified in the lower part of the section of sandstone and conglomerate in the Gollochy 
Burn, near Buckie. This is a true lava-flow ; he has observed pebbles of the rock in some of the 
overlying strata. With the exception of the Rhynie diabase already referred to, it is the only example 
yet noticed of the occurrence of contemporaneous volcanic rocks in the Lower Old Red Sandstone on 
the north side of the Grampian mountains, until we reach the far distant Shetland Islands. I have 
examined it microscopically, and find it to be identical in character with some of the lavas of the 
Lower Old Red Sandstone of central Scotland. It has a characteristic porphyry ground-mass through 
which are scattered decayed plagioclase crystals and numerous opaque ferruginous pseudomorphs, many 
of which appear to represent former augite. The characters of the volcanic rocks of the Old Red 
Sandstone will be described in a subsequent portion of this Memoir. [Since this Memoir -was read I 
have had an opportunity of examining the locality where this volcanic sheet occurs, and of confirming 
the view taken of its relations by Mr Wison. If we may judge from the different petrographical 
aspects of the mass, it would seem to consist of more than one flow, but with no intercalated tuff or 
other strata. ] 
