234> Murchisoris Silurian System. 



readers to infer, that the same beds of coal must be found at many 

 different levels, and they will doubtless also perceive that such dis- 

 turbances, added to the ascertained fact of the thinness of the coal 

 seams, must ever render the Brown Clee coal field of slight economical 

 value. 



The action of the wind in the galleries is checked by a pipe, one end 

 of which reaches the extremity of the working ground, and the other is 

 fixed in a "suff" to a vertical cylinder which rising to the surface ter- 

 minates at the pit mouth in a wooden trough-shaped funnel. The 

 result of this simple machinery is, that a strong column of air being 

 forced down this cylinder, the wind collected in the chambers is ex- 

 pelled by the shaft mouth, or in other words, an equilibrium is esta- 

 blished. 



It is believed by the workmen that the wind enters the galleries 

 through the cracks on the sides of the hills. The men at work at the 

 pit's mouth shelter themselves from the tempest by hurdles secured to 

 large blocks of basalt. 



The results of Mr. Murchison's views on the Salopian 

 coal fields are, that the Shrewsbury district was formed by 

 rivers emptying themselves into lakes, all the fossils being 

 fresh water and terrestrial. Coalbrook dale, which contains 

 a mixture of fresh water terrestrial and marine remains, 

 is referred to an estuary origin, while the Oswestry fields, 

 in which nearly all the animal remains are marine, were pro- 

 bably formed on the shores of an open sea. The observa- 

 tions of Macculloch and Hatchet distinctly prove that it 

 is the resinous principles of plants which mainly contri- 

 bute to the formation of coal ; and the geologist finds in the 

 most recent and superficial beds in which plants have been 

 buried the vegetable matter they contain to have lost 

 a portion of its original properties, approaching more or 

 less to the first stage of mineralization, termed brown coal. 

 Mr. Murchison refers to beds younger than the London 

 clay, in which vegetable bodies have been found in a con- 

 dition approaching to that of coal, and the Indian geolo- 

 gist will find hundreds of trunks of trees washed out 

 of the sands of the Bramaputra in Assam, in which the 

 form of the woody fibre and cellular tissue alone remains ; 



