94 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
were strongly folded with a general synclinal arrangement along an axis 
running roughly parallel to the Cobequid belt, the dips at South Jog- 
gins averaging 19° and in other parts from 0° to 45° or more (Plate 9). 
Strata characterized by such thickness and so diverse attitudes must 
have been covered by a constructional topography of relatively great 
strength. That topography is now lost, and a new one has taken its 
place. From the railroad station at Wentworth, one looks down over 
a vast expanse of this Carboniferous district and is struck by its even- 
ness (Plate 9). <A vast plain lies before the observer. It is highest at 
the three hundred-foot contour where it abuts against the Cobequids. 
Farther away, it sinks to an average elevation of two hundred feet, which 
persists throughout most of the basin, except where narrow valleys are 
incised below the plain. The plain is not absolutely level, but is gently 
rolling, as is typically displayed on the railroad from Maccan to South 
Joggins and along the Joggins shore. 
The rocks of the Colchester district differ from those of Cumberland 
in including only the Lower Carboniferous series and therewith a larger 
proportion of limestones than occur in the northern trough. The struc- 
tures are here more complicated. The beds stand at all angles to the 
horizontal plane and are frequently interrupted by faults of large throw. 
The great gorge at Truro affords an especially fine view of the steeply 
inclined sediments. The present topography is again, however, quite 
independent of structure. The lowland stands at an average height 
above the sea of about two hundred feet. Gentle ridge-like swells on 
the harder beds break the monotony of an otherwise nearly perfect 
plain, in which youngish valleys are sunk, comparable to those of 
Cumberland County. 
Now, in accounting for this great amount of denudation in both dis- 
tricts, we have not only to deal with a possible Jura-Cretaceous cycle and 
a possible Tertiary cycle; some place must be made for the enormous 
Permian denudation implied by the unconformity between the Carbo- 
niferous and the Triassic, and for Triassic denudation on unsubmerged 
Carboniferous. Then, too, a mid-Carboniferous period of subaerial con- 
ditions must have elapsed, since we find an unconformable relationship 
between the Lower and Middle Carboniferous strata. However, not- 
withstanding this latitude offered us in placing the dates of the various 
erosion-periods which, from time to time, have worn down the construc- 
tional Carboniferous relief, I have come to the belief that the existing 
lowlands owe their existence essentially to the same Tertiary cycle of 
wasting that explains for us the Annapolis Valley. 
