of Edinburgh, Session 1881 - 82 . 
601 
3. This lower cement-stone group is overlaid by a set of sand- 
stones, chiefly coarse brown and friable, with pebbles of white vein- 
quartz. These strata become more fossile towards the top, and 
contain courses of shale and bands of cement-stone. 
4. A second volcanic platform appears on this horizon. It 
consists sometimes of slaggy porphyrite, evidently a contempo- 
raneous outflow, and sometimes of a fine volcanic tuff. It can be 
followed for some distance from the valley of the Esk up Liddesdale. 
With it and a still higher volcanic zone should be associated the 
“ necks ” by which the older Carboniferous rocks of the district are 
pierced, and which no doubt represent some of the volcanic vents of 
the time. At the top of the tuffs comes a band of black cherts, 
which may perhaps be referable to the deposit of some thermal 
siliceous springs connected with the volcanic eruptions. 
5. This zone of fine grey shale, about 50 feet thick, is that which 
has yielded the remarkable series of fossils already described, and 
from which others since obtained have now to be brought to the 
notice of the Society. In the lower and central parts of the zone 
there occur numerous specimens of undoubtedly marine organisms, 
such as Orthoceras , Aviculopecten, My alma, Lingula , Discina and 
Palechinus. With these are mingled remains of fishes, crustacean 
and scorpions. Mr. Peach has observed, however, that towards the 
upper part of the bed where plants occur in some quantity, most of 
the Scorpions, Eurypterids, and Limuli have been discovered. 
6. A third zone of volcanic tuff 10 to 20 feet thick overlies the 
Eossiliferous or Scorpion Shales. This is the highest platform on 
which contemporaneous volcanic action has been observed in this 
part of Scotland. 
7. Above the third volcanic platform we enter upon a totally 
distinct type of strata — sandstones and shales with several bands of 
true crinoidal limestone, f exactly like those of the ordinary Car- 
boniferous Limestone, and containing many of the same fossils. 
These limestones form conspicuous features in the Esk below 
Canobie and at Penton Linns. One of them is 30 or 40 feet 
thick. Associated with them are seams of coal exactly as in the 
lower part of the Carboniferous limestone series of central Scotland. 
One of the most interesting features in this marine group is the 
evidence that it dies out towards the north-east in Liddesdale ; 
while, on the other hand, it increases in thickness towards the 
