!80 GENERAL VIEWS. 
and sandy ; frequently carbonaceous, so as to burn with flame and 
leave white ashes, and calcareous so as to effervesce with acids. All 
the plates whiten in fire, and are bleached near the Whin sill and 
dykes. Specific gravity 2 45 , 2 - 55 , 2 58 — altered by Whin sill Tees- 
dale 2*66. 
Shale . — The varieties of argillaceous rock, which are less finely 
and regularly laminated than plate, often of a lighter colour, some- 
times more sandy and micaceous and less calcareous, may be ranked 
under this name. It belongs rather to the millstone grit than to the 
mountain limestone formation. Specific gravity 2 - 4 , 2 ' 5 . Soapstone is 
a compact fine smooth-grained shale. 
Gray beds . — Alternations of plate or shale and laminated gritstone, 
too numerous and connected to allow of separate nomenclature, are use- 
fully characterized by this title, which also may comprehend such alter- 
nations as ‘ post and girdles,’ ‘ girdle beds’, ‘ stone bind,’ &c. These 
grow more abundant toward the North of Yorkshire, and appear more 
frequent in the millstone grit than in the Yoredale series. 
Flagstone. — -A laminated rock, composed of small worn grains of 
quartz, mica with or without felspar, and other minerals, occasionally 
calcareous, carbonaceous, and argillaceous: the mica or carbon lying- 
in particular planes causes the minute fissilitv of the stone, and bands 
of mica or argillaceous matter separate it into thin flags or beds. The 
tops and bottoms of gritstone rocks are often thus laminated ; plates 
becoming very sandy change to flagstone ; grit rocks becoming very 
argillaceous assume the same character : thus it is especially abundant 
in all parts of the Yoredale and millstone grit series, though its value is 
extremely variable. Vermicular markings, sometimes clearly of organic 
origin, often cover the surface, and indicate littoral deposition. Colour 
yellowish, black speckled, or white, the mica usually white and silvery. 
Specific gravity, Hutton roof 2 - 37 , 2 - 43 ; Brignall 2 50 ; Garsdale 2-52 ; 
Dent wold 2‘58 ; Ingleborough 2 - 60 . 
