GENERAL VIEWS. 
189 
limestone series, the Lammermuir must be passed by for its argillaceous 
materials are not of the nature required ; the Grampians, in this respect 
more suitable, can scarcely be admitted as the source of such rocks, else 
why do they not occur abundantly along its borders, and constitute a 
prominent feature among the Scottish limestones ? It is obvious that 
further inquiry would be of little value ; geology rejects conjecture ; 
but whether we imagine the materials to have drifted from the up- 
lifted Scandinavian Peninsula or from some ancient land or coast now 
lost in the ocean, the impression left on the mind is that great and 
extensive convulsions have since totally deranged the physical geography 
of the regions, and left no sufficient evidence for the guidance of a 
prudent theorist, in endeavouring to restore the lost hydrography of 
the sea which flowed above the mountain limestone deposits. 
These conclusions apply to the mountain limestone formation, let 
us see what can be learned of the millstone grit series by a similar 
investigation. 
The greatest thickness of the millstone grit series is found in York- 
shire ; it occurs in Nidderdale, Colsterdale, and about the head of Wens- 
leydale and Swaledale, as the details previously given have sufficiently 
made known. To the south of the line from Great Whernside to Bar 
fell, the series of millstone grit rocks, shales, and coal beds, appears to 
suffer condensation, and upon the whole to grow thinner, though the 
coarse pebbly rocks which characterize the series are even more abun- 
dantly deposited. Northward from Swaledale the whole series grows 
gradually thinner, the pebbly gritstones diminish and grow less im- 
portant, so that in the north-western parts of Northumberland it is 
doubtful whether they are worthy of a separate place in the scale of 
stratification. 
The greatest variety of substances occurs in the same parts of the 
country where the whole series has the greatest thickness ; perhaps the 
line of greatest variety may be drawn from Nidderdale head through 
Water crag. 
