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GENERAL VIEWS. 
Nature of the Rocks. 
The strata of the mountain limestone and millstone grit series are 
formed of limestone, chert, galliard, gritstone, flagstone, plate, shale, 
ironstone, and coal, variously combined 
Limestone . — Its chemical composition is remarkably uniform ; the 
thick beds of the whole series are nearly pure carbonate of lime ; 
but thin beds buried in thick deposits of clay (as in the country of 
Craven) are always contaminated by considerable admixture of argilla- 
ceous matter, and generally rendered unfit for the lime burner. The 
crystalline varieties contain magnesia. The aggregation of the rock 
varies ; it is compact, with smooth texture ; granular ; granular and 
crystalline, as in the beds and courses of dun lime ; oolitic as in the 
vicinity of Burton in Lancashire, composed of crinoidal columns as 
the Cam limestone generally. 
The different colours of the limestones offer curious subjects of 
inquiry ; the black varieties, sometimes certainly known to contain 
bitumen, are chiefly confined to the vicinity of argillaceous strata ; 
they occur at the top of the lower scar limestones alternating with 
plate; the Hardrow scar limestone and Simonside limestone are of 
dark or black colour almost universally ; certain thin beds between 
them are also dark coloured ; (these correspond to the black limestones 
of Craven and yield the Lent marble ;) the other limestones of the 
Y oredale series, and the thin beds above main limestone, are sometimes 
dark; — black and deep blue beds lie in the midst of the lower scar 
limestone in YY harfedale. Red limestone occurs in the lower scar 
limestone at Ravenstonedale, Kirby Stephen, Kirby Lonsdale, and 
Kettlewell : some of the limestone of Ash fell is yellowish : white 
limestone abounds in the midst of the lower scar series, where the 
beds are thick and the structure prismatic. Perhaps the most prevalent 
of all the varied hues of this rock is a bluish gray, of different degrees 
of intensity ; few beds are really blue, though the tendency to this 
colour increases to the northward, and the term is commonly used in 
