46 
SECTION OF THE PRIUTCHKA. 
and which are capped by the lowest beds of the mountain or carboniferous lime- 
stone, to be hereafter described. Whilst we refer to this woodcut for the general 
order and detail of the succession, we now 
confine our description to the strata be- 
neath the carbonaceous beds. 
The lowest beds visible (a) are green 
marl, with some remains of small fish- 
bones. These are separated from overly- 
ing red and green marls (c) by an inter- 
mediate course of sandstone ( b ) , which also 
contains fragments of minute fish-bones 
and ichtbyodorulites. 
The red and green mottled marls (c) , having a thickness of about thirty feet, are 
surmounted by the most remarkable “ bone-bed” (d) which ever fell under our ex- 
amination. This bed has altogether a thickness of about four feet, the upper part 
being a mottled, marly “ cornstone,” in which few remains exist, whilst the lowest 
part — a yellow marl about two feet thick — is almost entirely composed of bones 
and scales of ichthyolites. Of these, three species are pronounced by M. Agassiz 
to be identical with forms known in the Old Red Sandstone of Scotland 1 , viz. the 
Holopt y chius Nobilissimus (Ag., Sil. Syst.), Glyptosteus favosus (Ag.), Diplopterus 
macrocephalus (Ag.). Above the bone-bed is a whitish marly limestone (e) ten feet 
thick; then follow about sixty feet of red and green marly clay (/), with occa- 
sional harder courses, the whole being surmounted by the sands and bituminous 
schists which form the bottom of the Carboniferous system. 
The lowest of the carbonaceous strata is a thin band of yellowish marly incohe- 
rent sandstone ( g ), which here has not a greater expansion than six feet. In this 
bed, and in those above it, the carboniferous plants prevail, whilst the charac- 
teristic Old Red fishes are no longer to be detected in them. A line of physical 
demarcation is therefore neatly drawn between the Devonian and Carboniferous 
deposits. 
Range of the System to the North-east. — Having thus presented a general ascend- 
ing section of the Devonian or Old Red system in the region between Petersburgh 
1 The observations of Professor Agassiz on these identifications, and others to which we shall pre- 
sently allude, will be given in a subsequent part of the work (see also end of this chapter). 
7 . 
