42 THE DENUDATIONS OF NORTH WALES. 
all these directions these rocks form the floor on which the 
Carboniferous strata expose, and would have contributed their 
share of the débris; that the pebbles must therefore have been 
brought from the North or North-east, from an area intermediate 
between North Wales-and Cumberland, and. occupied not only 
by the newer strata, but now lying beneath the sea. But 
however this may be, I consider that the occurrence of this 
mass of pebbles, taken in connection with the metamorphism 
and cleavage exhibited by the Wenlock Shale and the extreme 
unconformity of the Carboniferous rocks upon it, are incontestable 
proofs that the Ludlow Beds and Tilestones once overspread the 
whole district from Central Wales across to the Lake District, 
but were denuded away from North Wales before the Curboni- 
ferous period, old as it is, had commenced. There can be no 
doubt that an unconformity such as this indicates the lapse of a 
great period of time. North Wales appears to have then 
formed portion of a continental area stretching far away to 
the North, mountainous and dotted with great lakes, for 
Proressor GEIkIE has shewn that the Grampians must have 
then existed as a mountainous range, providing material for the 
formation of conglomerates of extraordinary coarseness in the 
long arms of land-locked basins. During this continental period, 
the Lower Silurian rocks, with their interbedded ashes and lavas, 
came to be exposed at the surface, for we find that near Llan- 
dudno the Carboniferous Limestone rests directly upon them. 
But though no doubt these rocks, then as now, exhibited under 
the process of waste their characteristic scenery, it is more than 
doubtful whether any of the existing valleys can be traced back 
to that early period. The Carboniferous Basement Beds of 
North Wales, unlike the Old Red Sandstone in Scotland, shew 
no tendency to run up any of the present valleys. but seem 
rather to have been spread on a gently undulating plain, as a 
fringe round the high ground of Carnarvon. 
There now succeeded the great oceanic period in which the 
Carboniferons Limestone was deposited, followed by the estuarine 
and lagoon formations of the Millstone Grit and Coal-Measures ; 
a mass of strata exceeding 18,000 feet in North Lancashire, and 
probably not less than 6,000 feet in North Wales, and extending 
in an unbroken sheet over the whole district, with the exception, 
possibly, of the Carnarvon mountains. At the close of this long 
period of subsidence, elevation once more took place, denudation 
ensued, and some of the present features of the country began 
to cume into existence. The Carboniferous rocks were thrown 
into folds, and by the waste that took place along the lines of 
elevation, the Coal-Measures were separated up into distinct 
fields or basins. Along the line of the great bala fault or axis 
of upheaval not less than 4,o00 feet of strata were removed 
before the deposition of the New Red Sandstone, as is proved in 
the remarkable section near Hope Station, where this formation 
is seen resting on Millstone Grit. In the folds of depression, 
