On the Bitum inous Shales of Linlithgowshire, dec. 17 



his grand generalisation of the indication of the various 

 ages of the strata of central England, by their imbedded 

 fossils, demonstrated the coal-bearing strata to belong to a 

 system perfectly distinct from the Lias and Oolite lime- 

 stones and clays above, or his Greywacke system beneath. 

 But, by a precisely similar process of reasoning, he found 

 himself compelled to divide this system into several distinct 

 subdivisions. Vast masses of strata were found to cover 

 large tracts of country, which, though belonging to this 

 system, do not possess its valuable mineral characteristics. 

 The mountain limestone, — usually a single bed, which often 

 attains the thickness of a thousand feet, and whose bold 

 escarpments in the landscape include some of the most 

 romantic mountain scenery of England, — was made the 

 lowermost member of the series. A wild district of country 

 immediately betwixt this and the true Coal Measures, whose 

 chief rock was a gritty sandstone, served to mark out 

 the subdivision of the mill-stone grit ; and over this lay the 

 really industrially valuable beds of the series, the true Coal 

 Measures. As the nomenclature implies, this system was 

 an artificial one, adopted mainly for economic ends ; but it 

 adds a fresh lustre to the high genius of Smith, to find 

 that these subdivisions are also the same in a natural sys- 

 tem, which would express the various physico-geographical 

 changes which the strata, by our modern modes of geologic 

 elucidation, can be made to express. The Lancashire coal- 

 field most completely represents the various subdivisions of 

 the English carboniferous system ; and its development, as 

 well as its relation to the Scottish system, is represented in 

 the following table : — 



Vertical Section of Carbonifi 



England — Lancashire. 



1. Upper Coal Measures, 



2. Middle Coal Measures 



3. Lower Coal Measures, 



4. Millstone Grit, 



5. Toredale Bock Series. 



6. Limestone (no sedi 



mentary strata), 



Strata. 



Feet. 

 2,000 

 3,200 

 2,000 

 8,000 

 2,000 



2,000 



Total Sedimentary Strata, 12,200 

 VOL. III. 



Scotland— Lotliians. 



1. (Lost by denudation ?) 



2. Partially denuded, 



3. (Supposed to be absent.) 



4. Eoslyn Sandstofie Group, 



5. Edge-Coal Group, . 



6. Lower Carboniferous Se- \ 

 ries (shales and sand- f 

 stone with little lime- 1 



stone), ) 



Feet. 



1,000 



1,500 

 900 



3,000 



Total Sedimentary Strata, 6,400 

 c 



