XXVili Proceedings. 
alumina with the oxides of iron and manganese. They result 
from the decomposition of pumice and volcanic dust, either from 
terrestrial or submarine volcanoes. 
The extreme slowness of deposition is shown by the fact 
that the ‘Challenger’ frequently procured in a single haul hun- 
dreds of sharks’ teeth, some of them of gigantic size, and occa- 
sionally embedded in manganese ; dozens of ear-bones and other 
bones of whales, large numbers of manganese nodules, zeolites, 
and magnetic spherules, which are believed to be the dust of 
meteorites, which in the course of long ages have fallen upon the 
sea. Sharks and whales could never have been so numerous at 
one time that their remains should form a continuous stratum. 
Many generations would therefore be represented. 
The lecturer then compared chalk with Globigerina ooze, 
and also exhibited sponge spicules contained in the Greensand, 
and various specimens of Radiolarian earth which were com- 
parable with Radiolarian ooze. 
September 19th.—This meeting was devoted to the exhibition 
of specimens of interest, with brief descriptions of them. 
October 17th.—‘‘ On the Leonid Showers,”’ by James Edmund 
Clark, B.A., B.Se., largely illustrated by lantern slides :-— 
A meteor, in brief, is a minute particle of matter permeating 
the whole of space, subject to the same laws of gravity as our 
own earth. Like her, it is temporarily, at any rate, moving in 
an orbit round the sun with astronomical velocity measured by 
miles per second. The two orbits happen to intersect: the two 
bodies happen to come at the same instant to the point of inter- 
section, though the earth shifts its place by its own diameter 
every seven minutes. Most likely the meteor has been voyaging 
for the better part of a million years, since its last visit to us 
and the sun, and only for five minutes of this million years is it 
in danger of collision with the earth. And yet the collision 
comes. High up in the atmosphere the meteor, about the size 
of a mustard seed, and weighing at most, perhaps, a couple of 
grains, burns in an instant or two to impalpable dust. During 
this time it has traversed thirty to fifty miles, through atmo- 
sphere attenuated to almost an inconceivable degree. At the end 
it is rarely within thirty-five miles of the surface, and the 
air-pressure is still but one-thousandth of that at sea-level, or 
enough to raise the mercury in a barometer about 4; of an inch 
in place of 80 inches. ‘This pressure is less than the best 
vacuum from an ordinary air-pump. Most meteors vanish when 
still fifty miles high, having appeared at about seventy-five 
miles. At fifty miles the air is five hundred times rarer still ; 
at seventy-five the pressure is less than one-hundred-millionth 
a 
