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Mr. Weaver on the 
most parts of the island, we encounter ranges and groups of bold 
mountainous and hilly tracts, standing apart or isolated, while the 
interval between them is occupied almost invariably by a surface 
that appears nearly level when viewed upon the great scale, but 
which is found on nearer approach to present a gently undulated 
or varied line. A considerable expansion of this plain occupies the 
central counties of Ireland, and extends across the island from 
Dublin bay on the east to Galway bay on the west ; and it may be 
affirmed, almost without danger of error, that wherever a similar 
plain surface is observable the base consists of floetz limestone ; to 
the abundance of which mineral, next to the mild temperature and 
genial moisture of the climate, the soil of Ireland is probably more 
indebted for its superior fertility than to any other cause. It is a 
fact deserving notice, that with the solitary exception of Wicklow, 
there is no county in the island in which limestone rock, either of 
secondary or of primary origin, is not to be found ; but primary 
limestone appears in a great measure to be confined to the counties 
of Sligo and Galway, in the west, and to Donegal, Derry, Tyrone, 
and Antrim, in the north. 
§ 6. In the map, we perceive that mountainous and hilly 
tracts arise above the surface of the limestone plain, on the east, the 
south, the west, the center, and the north. 
§ 7. The Eastern chain constitutes a primary tract, extending 
from the north side of Dublin bay to the confluence of the Barrow 
with the Suire on the south ; (see Plate 6, No. 2.) It forms in 
its higher and central part a nearly continuous mass, until it is 
broken through by the river Slaney ; and farther south it is again 
interrupted by the pass of Scullogh Gap, separating Mount Lein- 
ster from Blackstairs, and by the river Barrow, which has divided 
the barrier that once connected Blackstairs with Brandon. The 
