22 
the series, representing in part at least, the middle Devonian slates and 
limestones of Plymouth and Ilfracombe. For this reason some have 
proposed to break up the system and allot its upper part to the carbon- 
iferous and the lower to the Silurian. But its continuous development in 
other localities, as well as the distinctive aspect of its organic remains, is a 
strong objection against so doing. 
The numerous thick sheets and dykes of trap intersecting the upper Old 
Red Sandstone in all directions afford ample evidence of internal igneous 
activity during its deposition. These become less frequent in its topmost 
beds, leading to the belief that the outburst gradually died away towards 
the time when the lower carboniferous strata were laid down. But the lull 
was only temporary: ere long the subterranean forces broke out again 
with all their former energy and the district was for ages subject to the 
occasional, perhaps the frequent, outpouring of trap, consisting in the 
earlier times of f elstone and in the later of basalt. Even after these out- 
flows ceased on the eastern, they continued on the western side of the chain, 
and the whole of the period corresponding in date with the age of our 
mountain limestone was marked in Linlithgowshire by stream after 
stream of greenstone from some crater of eruption as yet undetected and 
perhaps long ago destroyed by erosion. In a district so disturbed faults 
are of course abundant. The Pentland Hills are skirted by two along 
almost their entire length: one of these passes under the city of 
Edinburgh, near the Castle, and its throw is estimated at not less than 
2500 feet. Others intersect the coal-fields in all directions, and probably 
if the rest of the locality could be as thoroughly searched they would prove 
to be equally numerous in every part. 
Instead of the eighty feet of red and green shale with coprolite, &c, as in 
this neighbourhood, the base of the carboniferous system near Edinburgh 
consists of about 1000 feet of shale and calciferous sandstones with [inter- 
bedded and intruded trap. Of these strata, dipping at about 30 w to the 
East, the entire hill of Arthur's seat is composed, and the precipice of 
Salisbury crags is one of the intrusive igneous masses denuded and scarped 
by erosion. Both kinds of rock have been altered at and near the surface 
of junction, the sandstones being converted into quartzite and hornstone, 
and the shales having sometimes acquired a jaspery structure and appear- 
ance, while the trap itself has often become soft and friable in texture. 
In such a series organic remains are of course not very abundant. 
Those that occur belong to the lower carboniferous species of the district, 
Sphenopteris, Spirorbis, Rhizodus, Cypris, &c. I was also enabled through the 
