44 H. J. JOHNSTON-LAVIS ON THE GEOLOGY 
waves, and perhaps may not have been dissimilar to Stromboli. At 
the same time gradual elevation was going on, aided partly by the 
products of some of the neighbouring vents. 
The tufas underlying Monte Somma are proved to be of earlier date 
by the absence of leucitic rock-fragments in them. 
Of course these statements must be taken for the present as sug- 
gestive, and must necessarily either break down, or be confirmed by 
further evidence; but they furnish the most rational explanation, 
so far as facts are forthcoming. 
Scheme of the Eruptiwe Activity of Monte Somma and Vesuvius. 
‘¢ Introductory 
paroxysmal 
ee stage.— Pro- 
L blematical, 
| 
| Ancient _ Chronic ac- 
l ERA B. chronie ac- Puase I, pee a 
tivity. ot lava wit 
| scoria, ash, &e. 
( 4 Inactivity. 
rey, | | EE Denudation. 
ah . 
SOM 4 | Violent par- 
SOMME | Puase ITI. oxysm dwind- 
| ling into 
| Apparent 
turn ) 
| ( Apparentex- | Puase IV. eis: : 
| tinction inter- | chronie aeti- 
| ERA C 4 rupted by par- 4 a 
| . | oxysmal and Tnactivi 
; Other erup- | Puase V. vil 
\ tions Denudation. 
N . 
oxysmal erup- 
Violent par- 
tions. 
Puase VII. dwindling in 
| Less violent 
{ to 
—_— 
of lava, scoria, 
Moses Chronic ac- 
| &e. 
VESUVIUS. { ERA D. 4 chronie _ac- | Passe VIL 3 “vii. oil 
L | tivity. 
Puase I, 
Era of Permanent activity. 
The nearest approach that a geologist can make to the earliest 
ejectamenta composing the mountain is by means of the great 
craterial section of the Atrio del Cavallo. The lowermost beds of 
this escarpment present to us deposits that must have formed the 
surface of the cone, when its height could not have exceeded 1800 
metres in its completeness. Below this we cannot obtain any direct 
