262 
SILUEIA. 
[Chap. XI. 
coarse conglomerates on the sides of the mountain of clay-slate which 
flanks the Grampians, that these beds formed a passage into the Lower Old 
Red or Cephalaspis flagstones which undulate over Forfarshire and are 
surmounted by other red sandstones. 
In Banffshire, in 1859, I visited the banks of the Spey, and also Tynet 
Burn, where, through the kindness of Mr. Alexander Simpson, of Holl, I 
obtained a collection of fossil Pishes of the genera Pterichthys, Coccosteus, 
Glyptolepis, Osteolepis, Cheiracanthus, Diplacanthus, &c. As these are 
forms also known in Caithness, it is interesting to observe that the strata 
at Tynet lie far above the great mass of lowest Old Bed Sandstone ; they 
are, in faGt, like the Gamrie Ichthyolites, in the central zone of the group. 
Fossils (70). Old Eed Sandstone Fishes. 
1. Underside of Pterichthys cornutus, Agassiz, from Morayshire. 
(See the striking description of this Ichthyolite by its discoverer, Hugh Miller, 
in his ' Old Eed Sandstone,' p. 46.) 
2. Coccosteus decipiens, Agassiz, somewhat restored. 
(A perfectly restored head of this Pish is given in Mr. Miller's eloquent work, 
the ' Footprints of the Creator,' p. 50. Edinburgh, 1850.) 
The bituminous flagstones of Caithness and the Orkneys being thus con- 
sidered the central portion of this geological group, we may endeavour to 
see if there be any cause which may serve to explain why their imbedded 
Ichthyolites, so abundant in the north, should be so rare in the central and 
southern parts of Scotland. The explanation, it seems to me, is given in 
the fact that, as we proceed from north to south, the bituminous and cal- 
careous schists and flagstones so thin out that already in Nairn and Elgin, 
and still more at Gamrie, in Banff, such beds are represented by clays with 
nodules only, and that further southwards even these are no longer trace- 
able in the central portion of the sandstones. The condition, therefore, of 
