299 
Geological Relations of the East of Ireland . 
rocks are in these quarters almost wholly bounded by the floetz 
limestone plain ; but the debris of ' the limestone are intermingled 
with those of the primary substances, and they are distributed over 
the lower parts of the primary tract rising up the brows of the 
adjacent hills, penetrating into the vales that flank the central chain 
on the western side, occupying the inmost recesses, and ascending 
even a portion of the foot of the central chain itself ; debris of this 
nature may be observed all along the northern brow of the Dublin 
mountains, accumulated sometimes to the depth of one hundred 
feet and more; as for instance at the entrance of Glenismaule. 
These depositions have pierced even through Ballinascorney gap, 
and through the defile which separates the Tallow from the Rath- 
cool hills, into the narrow vallies in which the Liffey and its tribu- 
tary streams wind in the early part of their circuitous course. In 
the same manner, we find the base of the Glen of Imale, and the 
feet of the adjacent mountains, covered to a considerable depth by 
depositions of limestone gravel and marl; and the whole course of 
the valley of the Slaney, from granite through mica slate, and then 
through the granite flat into the clay slate country to the east, is 
marked by such deposits, until they gradually diminish to within 
three miles of Enniscorthy, when the limestone gravel wholly dis- 
appears ; but the marl continues diffused on both banks for a con- 
siderable distance down the river, particularly on the eastern side ; 
yet attaining to heights much above the present course of the 
stream. The vales of the Barrow, and the Nore, are marked by 
similar deposits, even after entering into the granite and clay slate 
tracts. These deposits are generally found on the salient angle of 
land formed by the bend of these rivers, and their, origin is quite 
evident, since the vallies, in which these streams flow* pass in the 
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