PROCEEDINGS OE GEOLOGICAL SOCIETIES. 
95 
tvreen 600° and 700° Fahr.) it loses its plasticity and acquires the property of 
rigidity. Moreover, having once lost its plasticity, this quality can never be 
restored to it by any methods known to science. Further, this property 
cannot be produced artificially. The constituent elements of pure clay 
may be combined in the proportions indicated by analysis, but the clay 
thus produced is not plastic. It is commonly stated that it is the alumina 
which confers upon clay its plastic property, but the author showed that 
pure alumina whether gelatinous, or after having been dried and ground up 
with water, never gives a plastic paste ; nor can water be the cause, since 
melted glass and seaHng-wax both possessed the property. 
The author considered that the phenomenon may be due to a change 
in the molecular arrangement of the particles of the clay, and the conse- 
quent variation of the attractive force which holds them together, — the 
particles, under the circumstances under which clay is plastic, being nearer 
to one another, and the attractive force consequently greater, than under 
the circumstances when the clay has the property of rigidity. 
As to the odour of clay, the author pointed out some difficulties in the 
way of the common opinion that alumina is the cause of this property, 
and sus^gested various considerations which might lead to the elucidation of 
this point. 
Liverpool Geological ^oqi-ety .-r-Jamutry 14. — The papers read 
were " On the Connection between Physical Geography and Geology." By 
F. P. Marrat. On the Geology of the Southern portion of the Isle of 
Man." By E. B. Franceys. 
February 11. — " On Surface-markings on the Sandstone near Liverpool, 
supposed to liave been caused by ice." By G. H. Morton, F.G.S. "A 
Brief Outline of the Geology of the country about Clitheroe, Pendle Hill, 
and Bromley." By G. H.' Morton, F.G.S. 
Manchester Geological Society. — December 31, 1861. — Mr. Bin- 
ney exhibited a specimen of granite containing petroleum, sent to him by 
James Yates, Esq., of London. The specimen was obtained in 1818, and 
is mentioned in Aiken's 'Mineralogy' (1815, p. 60), so that its discovery is 
of older date than thirty years ago. 
The papers read were : — 
1. " On the Ventilation of Mines." By Mr. Joseph Goodwin. The 
author considered that it was not new principles that were required to pre- 
vent the loss of life that is taking place year by year in the working of the 
coal-mines of this country, but attention to the simplest, oldest, and most 
commonplace precautionary measures. Nor were the evils arising from 
explosions the only ones to be guarded against ; it was alike a duty to pay 
attention to the sanitary state of the mines and to remove as far as prac- 
ticable all the causes which are life-destroying, or that injure the health of 
the operatives. The phenomena of sudden outbursts of gas, and the velo- 
city at which air-currents can be practically passed through the workings 
of a mine, were the chief topics of the paper. 
2. "On the Self-extinguishing and Detector Safety Lamp for working 
Mines." Bv Mr. George Charlton, Mining Engineer. 
January 28th, 1862.— Joseph Dickinson, Esq"^, F.G.S., President, in the 
chair. The following papers were read : — 
1. " On the Bank Top and Hagside Pits ; and the Proving of Faults." 
By Andrew Knowles, Esq. The Bank Top Collieries are about one mile 
from the town of Bury. One shaft or pit adjoins the East Lancashire sec- 
tion of the Lancashire and Yorkshire Eailway, and is connected with it 
by a siding ; the other is on the bank of the Manchester, Bolton, and 
Bury Caiaal, thp mine, the former pit is 130 yards deep, the latter 
