On the Bituminous Shales of Linlithgotvshire, (&c. 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 la}^ 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 Carboniferous Strata. 
England — Lancashire. 
1. Upper Coal Measures, 
2. Middle Coal Measures, 
3. Lower Coal Measures, 
4. Millstone Grit, 
6. Yoredale Rock Series. 
6. Limestone (no sedi 
mentary strata), 
Feet. 
2,000 
3,200 
2,000 
3,000 
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. Roslyn SandstOfie Group, 
5. Edge-Coal Group, . 
6. Lower Carboniferous Se- \ 
ries (shales and sand- r 
stone with little lime- 1 
stone), . . . ; 
Feet. 
1,000 
1,500 
900 
3,000 
Total Sedimentary Strata, 6,400 
c 
