CHAP. XXIII 
THE 
CARBONIFEROUS PERIOD IN BRITAIN 
here and tliere even growing into reefs. Foraminifera, sponges, sea-nrchins, 
brachiopocls, gasteropods, laniellil.mnchs and cephalopods, in many genera 
and species, mingled their remains with the dead crmoids^ and coials to 
furnish materials for the wide and thick accumulation of Carboniferous 
Limestone. . , , , 
Looking broadly at the history of the Carboniferous period, and hearing 
in mind the evidence of prolonged depression already referred to, we can 
recomiize in it three great eras. During the first, the wide cle^ir sea of tie 
Carboniferous Limestone spread over the centre and south ot Lritain intei- 
rupted here and there by islands that rose from long ridges whereby the sea- 
floor was divided into separate basins. Next came a time of lessenec 
depression, when the sea-bottom was overspread with sand, mud and gravel, 
and was even in part silted up, as has been chronicled in the Millstone 
Grit. The third stage brings before us the jungles of the Coa -measures, 
when the former sea-lloor became a series of shallow lagoons where, as in 
the mangrove-swamps of our own time, a terrestrial vegetation sprang up 
and miiiMed its remains with those of marine shells and fishes. 
Such a state of balance among tlie geological forces as is indicated by 
the stratigraphy of the Carboniferous system would not prepare us lor the 
discovery of the relics of any serious display of contemporary volcanic 
activity And, indeed, throughout the Carboniferous rocks of Western 
Europrthere is for the most part little trace of eonteniporaiieous volcanic 
eruptions. Yet striking evidence exists that, along the western borders of 
the continental area, in France as well as over much ot Dritaui, which had 
for so many previous geological ages been the theatre of subterranean activitj, 
the older half of Carboniferous time witnessed an abundant, though less 
stupendous and prolonged, renewal of volcanic eiierg}. . , , , 
From the very eomniencenient of the Carboniferous period to the epoch 
when the Coal-measures began to be accnmulated, the area of the Britis i 
Isles continued to be a scene of active volcanism. In the course of that 
prolonged interval of geological time the vents shifted their positions, 
and o-radually grew less energetic, but there does not appear to have been 
any protracted section of the interval wlien the subterranean activity became 
everywhere entirely ipiiescent. „ • 
The geologist who traces, from older to younger formations, the progress 
of some persistent operation of nature, obsen es the e\ ic ence if*! 
increase in amount and clearness as it is furnishec ij successne y 
parts of the record. He finds that the older rocks have generally been so 
dislocated and folded, and are often so widely covered by younpr loimiatioiis, 
that the evidence which they no doubt actually contain iiiaj ® ° 
decipher, or may be altogether concealed from view. In following for 
instance, the progress of volcanic action, he is impressed, as he passes irom 
the older to the younger Falaiozoic chronicles, by the striking coutia.s 
between the fulness and legibility of the Carboniferous _ records and the 
comparative meagreiiess and obscurity of those ot the earlier perio s. ^ le 
Carboniferous rocks have undergone far less disturbance than tlie Cambrian 
