PEOCEEDlJfGS OF GEOLOGICAL SOCIETIES. 



95 



tween 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 knoTvn 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 sealing-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 suggested various considerations which might lead to the elucidation of 

 this point. 



LiYEEPOoL Geological Society. — January 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 have 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." By Mr. George Charlton, Mining Engineer. 



January 2Sth, 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 Cartal, To the mine, the former pit is 130 yards deep, the latter 



