182 } THE OLD RED SANDSTONE. 
of the strongly impregnated rocks and clay-beds of this for 
mation, like the bitumen of the still more strongly impreg:- 
nated limestones and shales of the Lias, seems to have had 
rather an animal than vegetable origin. ‘The shales of the 
Eathie Lias burn like turf soaked in oil, and yet they hardly 
contain one per cent. of vegetable matter. Ina single cubic 
inch, however, I have counted about eighty molluscous 
organisms, mostly ammonites, and minute striated scallops ; 
and the mass, when struck with the hammer, still yields the 
heavy odor of animal matter in a state of decay. The lower 
fish-beds of the Old Red are, in some localities, scarcely less 
bituminous. ‘The fossil scales and plates, which they enclose 
burn at the candle; they contain small cavities filled with a 
strongly scented, semi-fluid bitumen, as adhesive as tar, and 
as inflammable ; and for many square miles together the bed 
is composed almost exclusively of a dark-colored, semi-calca- 
reous, semi-aluminous schist, scarcely less fetid, from the 
great quantity of this substance which it contains, than the 
swine-stones of England. Its vegetable remains bear but a 
small proportion to its animal organisms; and from huge ac- 
cumulations of these last decomposing amid the mud of a 
still sea, little disturbed by tempests or currents, and then sud- 
denly interred by some widely spread catastrophe, to ferment 
and consolidate under vast beds of sand and conglomerate 
the bitumen* seems to have been elaborated. These bitu- 
minous schists, largely charged with sulphuret of iron, run 
far into the interior, along the flanks of the gigantic Ben We- 
* «In the slaty schists of Seefeld, in the Tyrol,” say Messrs. Sedg- 
wick and Murchison, “there is such an abundance of a similar bitu- 
men, that it is largely extracted for medicinal purposes.” — (Geoh 
Trans. for 1829, p. 134.) 
