DENUDATION IN NOVA SCOTIA. 
417 
ing the globe, and that diifereiit currents of air varied then 
as now in teraiDerature, so as to give rise, by their mixture, 
to the condensation of aqueous vapor. 
Fig. 444. Fig. 445. 
Fig. 444. Carboniferous rain-prints with worm-tracks (a, 5) on green shale, from Cape 
Breton, Nova Scotia. Natural size.—Fig. 445. Casts of rain-prints on a portion of 
the same slab (Fig. 444), seen to project on the under side of an incumbent laj^er of 
arenaceous shale. Natural size. The arrow represents the supposed direction of 
the shower. 
Folding and Denudation of the Beds indicated by the Nova 
Scotia Coal-strata. —The series of events which are indicated 
by the great section of the coal-strata in ISTova Scotia consist 
of a gradual and long-continued subsidence of a tract which 
throughout most of the period was in the state of a delta, 
though occasionally submerged beneath a 
depth. Deposits of mud and sand were 
first carried down into a shallow sea on the 
low shores of which the foot-prints of rep¬ 
tiles were sometimes impressed (see p. 407). 
Though no regular seams of coal were 
formed, the characteristic imbedded coal- 
plants are of the genera Cyclopteris and 
Alethopteris^ agreeing with species occur¬ 
ring at much higher levels, and distinct 
from those of the antecedent Devonian 
group. The Lepidodendron corrugatum 
(see Fig. 446), a plant predominating in 
the Lower Carboniferous group of Europe, 
is also conspicuous in these shallow-water 
beds, together with many fishes and ento- 
mostracans. A more rapid rate of subsidence sometimes con¬ 
verted part of the sea into deep clear water, in which there 
18 * 
sea of moderate 
Fig. 446. 
Cone and branch of 
Lepidodendron corru- 
fiatum. Lower Car- 
boiiiferous, New 
Brunswick. 
