MODIFIED by COMPRESSION. 167 
pless Andcut-thus appears, that whinftone poflefles all the pro- 
rile which we are led by theory. to afcribe to an imternal 
lava. bet ni 
Tuts: conection “is sir aliciitesed by an cieiididie 
cafe between the refults of external and ifternal-fire, difplayed 
incan:aGual fection of the ancient part of Vefuvius, which oc- 
curs in the Mountain of Somma mentioned above. I formerly 
defcribed. this {cene in my paper on Whinftone and Lava; and 
I muft beg leave once more to prefs it upon the notice of the 
public, as affording to future travellers: a) moft interefting field 
of geological inquiry. 
Tue fection is feen in the ie ssiibick cliff, feveral hundred 
feet in: height, which Somma prefents to the view from the 
little-valley, in form of ‘a crefcent, which lies. between Somma 
and the interior cone of Vefuvius, called the Atrio del Cavallo. 
(Figs 42. reprefents ithis :feene, done from the recollection of 
whatrI: faw in-1785.) abc is the interior cone: of Vefuvius; 
af g the mountain’ of Somma; and ¢de the Atrio del Cavallo). 
By means of this cliff. (fd in figure 42. and which is repre- 
fented ‘feparately in fig.\44:); we fee the internal ftru@ture of 
the mountain, ‘compofed of :thick beds (#4) of loofe fcoria, 
which have fallen in fhowers; hetween which thin but firm 
ftreams: (m m) of lava are interpofed, which have flowed down 
the outward conicalfides of the mountain. (Fig. 43. is an ideal 
{éGon of Vefuvius and Somma, through the axis of the cones, 
fhewing;the:manner in which: the beds. of fcoria and: of lava 
lie upon each other; the extremities of which beds are feen 
edgewife inthe, cliff at mm and hk, fig. 42, 43, and’ 44.). 
Tuts aflemblage-of feoria and lava is traverfed abruptly and 
vertically by (ftreams: of folid. lava (a2, fig, 44.), reaching 
from top to bottom of the cliff. Thefe laft I conceive to have 
flowed in rents of the ancient mountain, which rents had acted 
as 
