356 
THE CARBONIFEROUS VOLCANOES 
BOOK VI 
conditions alternating along the margins ot the sinking land, according as 
the rate of depression surpassed or fell short of that of the deposition of 
sediment. There is no trace of any general disturbance among the strata, 
such as would he marked by an important and widely extended uncon- 
formahility. But many indications may be observed that tlie rate ot 
subsidence did not continue uniform, if, indeed, the downward movement 
was not locally arrested, and even exchanged for a movement in the opposite 
direction. Tt is difficult, for instance, to believe the ancient ridge of the 
klidlands to have been so lofty that even the prolonged subsidence required 
for the accumulation of the whole Carboniferous system was insufficient to 
carry its highest crests below the level of the coal-jungles. More probaldy 
the depression reached its maximum along certain lines or hands running in 
a general nortli-easterly direction, the intervals between these lines sinking 
less, or possibly even undergoing some measure of uplift. One of the sub- 
siding tracts, that of the wide lowlands of Central Scotland, was Hanked on 
the south by a ridge which, while its north-eastern portion was buried under 
the Upper Old Bed yaudstone and Lower Carboniferous rocks, remained 
above water towards tlie south-west, and does not appear to have Ireen 
wholly submerged there even at the close ot the Carboniferous period. 
So almndant and varied are the sedimentary formations of Carboniferous 
time, and so fully have they preserved remains of the contemporary plants 
and animals, that it is not difficult to realise in -some measure the general 
aspect of the scenery of the time, and the succession of clianges which it 
underwent from the beginning to the end of the period. The land was 
green with a luxuriant if somewliat monotonous vegetation. Large pine 
trees flourished on the drier uplands. The lower grounds nourished dense 
groves of cycads or plants allied to them, which rose as slim trees twenty or 
thirty feet high, with long hard green leaves and catkins that grew into 
berries. The swamps and wetter lauds bore a rank groAvth of various gigantic 
kinds of club-moss, equisetaceous reeds and ferns. 
Nor was the hum of insect-lite absent Iroiii these forests. Ancestral 
types of cockroaches, mayflies and beetles lived there. Scorpions swarmed 
along the margins of the shallow waters, for their remains, washed away 
with the decayed vegetation among which they harboured, are now found 
in abundance throng! lout many of the dark shales. 
The waters were haunted by numerous kinds of fish quite distinct from 
those of the Old Bed Sandstone. In the lagoons, shoal.s of small ganoids 
lived on the cyprids tiiat peopled the bottom, and tliey were in turn preyed 
on by larger ganoids with massive armature of bone. Now and then a 
shark from the opener sea would find its way into these more inland waters, 
d'he highest types of animal life yet known to have existed at this time were 
various amphibians of the extinct order of Labyrinthodonts. 
The open sea, too, teemed with life. Wide tracts of its floor supported 
a thick growth of crinoids whose jointed stems, piled over each other 
generation after generation, grew into masses of limestone many hundreds 
of feet in thickness. Corals of various kinds lived singly and in colonies. 
