424 Editorial Comment. 
* 
at the Avon gorge, below the city of Bristol, where the river 
has cut a channel 300 feet deep, exposing several thousand feet 
of strata, the section extending from the Old Red sandstone near 
its base to the coal measures, the upper part being repeated by 
a fault having a throw of 800 feet, and passing across the gorge 
nearly at right angles. 
Monday's session was, for the most part, occupied with a 
series of papers by Drs. Anderson, Johnston-Lavis and Claypole 
on various points more or less directly bearing on volcanic phe- 
nomena. Much interesting material was brought forward, and 
a lively discussion maintained. The first-named author showed 
by the lime-light a set of photographs of the volcanoes of the 
two Sicilies. These were very good and elicited general admi- 
ration . Dr. Johnston-Lavis read a letter received by him from 
a friend, describing vividly an eruption of Volcano in August 
last, when, after a sudden suspension of activity, red hot stones 
were thrown out to the distance of three-fourths of a mile, some 
of which measured 15 yards in length. One of less size fell 
through the roof of his house. Another, four feet in diameter, 
dropped close by him as he left his home, and, broken by the 
fall, burned his children's feet. Hundreds of others were scat- 
tered over the slopes or fell back into the crater of the volcano. 
The same observer also noted the occurrence of metallic iron in 
a Vesuvian lava, and of leucite in a lava from Etna. 
In the evening a lecture was delivered by Prof. T. G. Bon- 
ney on " The Foundation Stones of the Earth's Crust." The 
subject was the structures of the so-called primitive rocks, the 
gneisses, etc., of which the oldest known beds are composed. It 
was, of course, impossible, in such an address, to enter into min- 
ute points of detail, and the speaker very wisely confined him- 
self to laying before his audience, with the aid of a lantern, the 
basal facts on which the new science of petrology rests. He 
showed clearlv the difference between a gneiss, with its confused 
and uncrystalline appearance, and a true granite, showing the 
rectilinear edges of its crystalline elements. He then passed on 
to the effects of pressure on these foundation stones, taking the 
ground that pressure alone does not produce structural change, 
but that such structural changes are due to shearing movements 
in the rock, which behaves like an imperfect liquid. In this 
way mica plates and scales are developed from feldspar, and layers 
