130 
ELEMENTS OF GEOLOGY. 
Fig. 84. 
1 -^--^ 1 
In another diagram, Fig. 85, a real section of the geologic¬ 
al formations in the neighborhood of Bristol and the Mendip 
Hills is presented to the reader, as laid down on a true scale 
by Professor Ramsay, where the newer groups 1, 2, 3, 4 rest 
unconformably on the formations 5, 6, V, and 8. At the 
southern end of the line of section we meet with the beds 
No. 3 (the New Red Sandstone) resting immediately on Nos. 
7 and 8, while farther north, as at Dundry Hill in Somerset¬ 
shire, we behold eight groups superimposed one upon the 
other, comprising all the strata from the inferior oolite, No. 
1, to the coal and carboniferous limestone. The limited hor- 
Fig. 85. 
Section South of Bristol. (A. C. Eamsay.) 
Length of section 4 miles. a, 1 ). Level of the sea. 
1. Inferior Oolite. 2. Lias. 3. New Eed Sandstone. 4. Dolomitic or magnesian con¬ 
glomerate. 5. Upper coal-measures (shales, etc.). 6. Pennant rock (sandstone), 
t. Lower coal-measures (shales, etc.). 8. Carboniferous or mountain limestone. 
9. Old Eed Sandstone. 
izontal extension of the groups 1 and 2 is owing to denuda¬ 
tion, as these formations end abruptly, and have left outly¬ 
ing patches to attest the fact of their having originally cov¬ 
ered a much wider area. 
In order, therefore, to establish a chronological succession 
of fossiliferous groups, a geologist must begin with a single 
section in which several sets of strata lie one upon the other. 
He must then trace these formations, by attention to their 
mineral character and fossils, continuously, as far as possible, 
from the starting-point. As often as he meets with new' 
groups, he must ascertain by superposition their age relative¬ 
ly to those first examined, and thus learn how to intercalate 
them in a tabular arrangement of the whole. 
By this means the German, French, and English geologists 
