Page:The Geologist, volume 5.djvu/119

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 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 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 consequent 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.

.—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.

.—December 31, 1861.—Mr. Binney 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 prevent 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 practicable all the causes which are life-destroying, or that injure the health of the operatives. The phenomena of sudden outbursts of gas, and the velocity 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 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 section of the Lancashire and Yorkshire Railway, and is connected with it by a siding; the other is on the bank of the Manchester, Bolton, and Bury Canal. To the mine, the former pit is 130 yards deep, the latter