ANNIVERSARY ADDRESS OF THE PRESIDENT. IxxXlil 



Apennine limestone. The external truncated cone is composed, ac- 

 cording to Dr. Daubeny, who visited the locality, of an earthy vol- 

 canic tuff mixed with mica and occasionally pumice ; a red ferrugi- 

 nous variety is sometimes seen in beds, alternating with the more 

 common kind, and in one instance forming a kind of vein running 

 vertically through the strata. 



The external cone rises with a gentle slope from the base, attaining 

 near the summit an inclination of 18°. The brim is more than 2000 

 feet high, and is complete throughout half the circumference, this 

 portion of the original crater remaining perfectly intact. This 

 part of the mountain is called Monte Cortinella, and by the map it 

 appears to be continuous for more than three-fourths of the circum- 

 ference, and Dr. Daubeny says that it may be traced in other parts 

 throughout its entire circumference, except in one place. The outer 

 brim is covered over with loose or compacted aggregates of vol- 

 canic sand, and of stones promiscuously heaped one upon the 

 other. Blocks of a kind of porphyry, composed of a decomposing 

 felspar, including large crystals of leucite and minute crystals of 

 augite, are often imbedded in the tuff, and a little below the ex- 

 ternal margin there is a bed of this leucitic porphyry continuous 

 for some distance. The external cone has a steep inner escarp- 

 ment, forming the crater, enclosing a great plain, from the centre 

 of which rises the conical mount of Santa-Croce, about three- 

 quarters of a mile in diameter at its base, and rising to a height of 1082 

 feet above the inner plain, towering considerably above the brim of 

 the crater at its highest point, in the Monte Cortinella. The plain 

 is thus about three-quarters of a mile broad between the base of 

 Santa-Croce and the escarpment. These measurements are not all 

 contained in the memoir of Dr. Daubeny, they are partly taken from 

 that of M. Pilla. The summit of the conical hill is exactly equi- 

 distant from all parts of the crest of Monte Cortinella. It is com- 

 posed of a fine-grained compact rock, a trachyte containing much 

 mica, and Dr. Daubeny assumes that the whole hill is composed of 

 this rock ; but as he tells us that, abrupt as it is, it is everywhere 

 covered with vegetation, it is possible that it may not be of so simple 

 a composition ; a doubt I may be permitted to express, as he lays 

 so much stress on the structure of this interior mount, in his theory 

 of the formation of the group. 



M. Abich, M. Pilla, and Dr. Daubeny agree in considering Rocca 

 Monfina as a very perfect example of a crater of elevation. Dr. 

 Daubeny thus expresses himself: — "The circumstance which, in a 

 geological sense, attaches the highest interest to the structure of this 

 mountain, is the support which it appears to afford to the theory of 

 elevation.'' — *' A conical mass of rock so considerable, and yet so 

 completely circumscribed within the area of the crater, could only, 

 as it would seem, have been brought into the position which it is 

 seen to occupy, by being upheaved all at once from the interior of 

 the globe, whilst in a semi-fluid or pasty state, but not in a condi- 

 tion of actual liquidity." — " Alternating strata of tuff and lava may 

 indeed be imagined to build up in the course of time a mountain of 



VOL. III. g 



