VALLEY OF THE ARDECHE—LA BEAUME. 9 
heat being gradually spent, the currents have lost their mobility, and do not at 
all extend themselves into the plains. When we trace these lava currents to 
their sources, the result is uniformly the discovery of a crater, often formed in 
the breast of a mound of cinders, whose fiery-red colour will bear a comparison, 
in point of apparent freshness, with any of those which stud the flanks of Vesu- 
vius,; or the more prolific Etna; and, in very many instances, the precise point of 
ejection of the lava may be ascertained with the most extreme nicety, and all 
the accidents of its subsequent course chronologically traced. Thus, every indi- 
vidual eruption has written, as it were, its own history, although the relative 
dates cannot always be determined. It is an inquiry not a little interesting (at 
least upon the spot) to collect these rude hieroglyphics, which form a chapter of 
the ancient records of our globe, and register events amongst the most recent of 
geological change, yet of which no trace or tradition is to be found amongst the 
histories of the Gallic nations. 
The hamlet of La Beaume lies on the right bank of the Ardéche, almost 
under the shadow of a basaltic colonnade, which stretches parallel to the course 
of the river, but leaves a level space between the foot of the cliff and the 
water, along which the public road passes. The section (Plate IL., fig. 3) is suffi- 
ciently remarkable to have attracted attention ever since the days of Fausas St 
Fonp, who has given a view of it, but with great inaccuracy and exaggeration. 
Our figure shews the lava stream (a) invested with a coating of soil, on which is 
abundant vegetation. The lava rests on a mass of scoriz , which again reposes 
upon the debris and vegetable mould c, thus marking strongly the comparative 
recency of the eruption which produced the lava, and the perfectly natural and 
modern condition of the valley into which it flowed. The debris and soil rest 
upon the primitive rock (granite or gneiss) which is exposed in the bed of the 
river Ardéche. 
The contact of the lava and scorie (beds a and 4) presents some interesting 
considerations; and, jirst, to account for the so frequent phenomenon of the 
superposition of lava to the scorize, which, being its scum and refuse, we should 
rather expect to find upon its surface, we must recall the peculiar manner 
of progression of those highly viscid lavas, which most abound in scoriz (for, 
whilst very fiuid, there is little or no scoria deposited). The progression is ex- 
ceedingly slow, and, according to the usual laws of a tenacious fluid, moving 
over a rough surface with great friction, the surface moves faster than the bottom 
of the stream, and the front of the wave of lava (that which would be presented 
to a spectator towards whom it is in the act of descending) being hard and scori- 
aceous, in consequence of long exposure to the cooling action of the air, is con- 
tinually thrust wnder the liquid as it slowly struggles on, and its place is supplied 
by freshly floating scum from the surface, which finally descends the front of 
VOL. XX. PART I. Cc 
