and the other Azores. 959 
portion of the work which although highly interesting has been 
sn part published before. In this chapter is a letter from 
Captain Tillard of the British frigate Sabrina, ‘ describing 
the phenomena attending the eruption from the sea in 1811, 
and which was originally published in the Philosop. Transact. 
for 1812. The frigate being there at the time, Capt. T. 
landed on the new island and named it “ Sabrina,” but it 
disappeared a few days after beneath the waters of the 
ocean. ‘To the account of Capt. T. succeeds another, first 
published in the ninth volume of Brande’s Jour. of Science 
and the Arts, of the Royal Inst. 
We observe Dr. Webster makes much use of the word 
Trachyte, which is rather new in this country. This term 
is now applied very generally abroad to a porphyritic rock, 
or rather, to many different porphyritic rocks having the 
general character of containing crystals of glassy felspar. 
In speaking of this rock, it is observed in the Edin. Ph. 
Jour. ina paper of Dr. Borré’s on the volcanic rocks of 
Auvergne, that “ it is almost impossible to give a definition 
of such a rock; how could it be otherwise with a volcanic 
production, which is formed from all the different members 
of the granite formation ?” 
Pumice is described as occurring in vast quantity and it 
often contains bituminous wood resembling the Suturbrand 
of Iceland. A distinct transition from Pumice to Obsidian 
was often noticed. The obsidian is always found in St. Mi- 
chael, in loose pieces and is of the usual black colour, some- 
times irridescent, which Dr. Webster attributes to exposure 
to the air, &c. and always contains crystals of glassy felspar. 
In chap. XIV, an interesting account is given of a stu- 
pendous crater fifteen miles in circumference, and now em- 
bosoming an inland lake which covers one third of the in- 
cluded space, while the rest is occupied by vegetables and 
a thin population with a small village called by the natives, 
the seven cities, and the vale is called the valley of the sev- 
en cities; — ~ 
In the XVth chapter a remarkable rock is described as 
eccurring on the mountain of Agoa de Pao. ‘Some of 
the pieces were about twice the size ofa man’s head, and, 
at first sight, might easily have been mistaken for pieces of 
granite. They are composed of felspar and hornblende, 
and contain a few scattered grains of magnetic iron. The 
