
722 STRATIGRAPHICAL GEOLOGY. — [Boox VI. 
eoal-growths. From the fact that a succession of coal-seams, each 
representing a former surface of terrestrial vegetation, can be seen in 
a single coal-field extending through a vertical thickness of 10,000 
feet or more, it is clear that the strata of such a field must have been 
laid down during prolonged and extensive subsidence. It has been 
assumed that besides depression, movements in an upward direction 
were needful to bring the submerged surfaces once more up within the 
limits of plant-growth. But this would involve a prolonged and 
almost inconceivable see-saw oscillation; and the assumption is 
really unnecessary if we suppose that the downward movement, 
though prolonged, was not continuous, but was marked by pauses, 
long enough for the silting up of lagoons and the spread of coal- 
jungles. yaa 
Life.—Each of the two phases of sedimentation just described 
has its own characteristic organic types, the one series of strata 
presenting us chiefly with the fauna of the sea, the other mainly 
with the flora of the land. The marine fauna is specially rich in 
crinoids, corals, and brachiopods, which of themselves constitute 
entire beds of limestone. Among the lower forms of life some genera 
of foraminifera have a wide extension; Saccammina, for example, 
forms beds of limestone in Britain, and Fusulina plays a still more 
important part in the Carboniferous Limestone of the region from 
Russia to China and Japan, as well as in North America, while 
Nummulina occurs in the Belgian limestones. The corals are 
represented in the English Carboniferous Lime- 
stone by some thirty genera, including about 
100 species belonging to tabulate (Kavosites, 
Michelinia, Alveolites, Choetetes), and still more 
to rugose forms (Amplewus, Zaphrentis, Cyatho- 
phyllum, Aulophyllum, Clisiophyllum, Lithostro- 
tion, Lonsdaleia, Phillipsastrea). The HKehino- 
; derms are abundant and varied. Thus among 
=» the urchins of the Carboniferous seas were specie 
3 ~=— sof Archxocidaris, the plates and spines of which 
are of frequent occurrence. The blastoids or 
pentremites, which now took the place in the 
| Carboniferous waters that in Silurian times had 
Fic. 335.--Canpon- been filled by the Cystideans, attained their 
oN apne CrINolD, maximum development. But it was the order 
“Teme. a eta of crinoids that chiefly swarmed in the - geas 
arnmet abla parto? where the Carboniferous Limestone was laid 
ee enc the down, their separated joints now mainly com- 
column-jointsshowing SOROS solid masses of rock name: hundreds of 
sted nana: feet in thickness. Among their most conspicuous 
genera were Platycrinus, Cyathocrinus, Poterio- 
erinus, Tthodocrinus, and Guilbertsocrinus. 'lubicolar annelides 
abounded, some of the species being solitary and attached to shells, 
corals, &c., others occurring in small clusters, and some in eregarious 


