340 
PROCEEDINGS, 1859 — 1870. 
near Leeds, introduced a new Hydraulic Coal-cutting Machine to the 
members. It was manufactured by Messrs. Garrett, Marshall & Co., 
of Leeds, and was then at work at Kippax. The machine was worked 
by water pressure, produced b)^ an engine placed at the bottom of 
the shaft. The pressure employed varied from 150 to 300 pounds 
per square inch. It had an 18 inch stroke, and made 25 strokes per 
minute, using in that time 40 gallons of water. The cutting bar is 
furnished with three cutters, which effected at one stroke a depth of 
3 feet 3 inches. As much as 39 feet in length on the face of the 
coal had been cut in the above depth in an hour. The cost was less 
than half that of getting coal by hand labour. The produce of slack 
was very much less, and the net result was a saving of lOjd. per ton 
upon the produce. 
Mr. Sorby contributed a paper on Impressed Limestone Pebbles, 
as illustrating a new principle in chemical geology. Much attention 
had been drawn on the continent to the curious phenomenon of one 
pebble penetrating another, sometimes to such an extent that it 
nearly passed through it without there being any apparent fracture. 
Mr. Sorby considered tliat this must be explained by the convertibility 
of mechanical pressure into chemical action, the pebbles being pressed 
one against the other with great force at a considerable depth below 
the surface of +he earth, and surrounded with water saturated with 
Carbonate of Lime the limestone would dissolve, so that in time one 
pebble would penetrate into the other, and Carbonate of Lime would 
be deposited in a crystalline form elsewhere, where the pressure was 
less. 
In October, 18(57, at a meeting held at Barnsley, Mr. A. H. 
Green, M.A., of H.^I. Geological Surve}', read a paper on the 
Geology of the Barnsley Coal-field. The rocks in this district of 
Yorkshire consist of Coal Measures, Millstone Grit, and Mountain 
Limestone. The latter is a mass of pure Limestone, of great but 
unknown thickness, with very few thin layers of interbedded shale, 
and two or three beds of lava and volcanic ash. The latter are inter- 
bedded with the Hmestone, and must, therefore, have been deposited 
during its formation. The limestone is very fossiliferous, and wasformed 
in a clear sea, unstained by mud. In the course of time the sea-bottom 
