18 Messrs. Faraday and Lyell on 



teen years during which the pit has been opened. The chief 

 danger to be guarded against, arises from what are termed 

 *' caldron bottoms," which are the stools or lowest portions 

 of erect fossil trees, filled with sandstone or shale, and having 

 their bark converted into coal, which gives way when they are 

 undermined, and allows the heavy cast of the interior of the 

 trunk, several feet or yards in height, to descend suddenly. 

 The Hutton seam rests on a sandy clay, which has not been 

 found adapted for a fire clay. The floor composed of it does 

 not often rise in creeps. 



It will be seen by the section, that several upper seams of 

 good coal, the united thickness of four of which is no less than 

 13 feet, have been left untouched, in order that the thicker 

 and more valuable seam called the Hutton, should first be 

 worked out. In adopting this plan, the proprietors have been 

 guided by considerations of present profit, which the compe- 

 tition of other neighbouring coal works renders indispensable. 

 Nevertheless, it may not be improper for us to advert to two 

 evils which result from this system. 



First. The upper seams which are undermined on the ex- 

 traction of an inferior bed of coal, sink down, often unequally, 

 from failure of support, and become fractured, and therefore 

 much more liable to give out gas, which gas (it is well known 

 by experience) has sometimes found its way into the workings 

 far below, as attested by Mr. Buddie in his evidence given to 

 the Committee of the House of Commons in 1835; by which 

 some of the most serious accidents from fire-damp have been 

 occasioned. The greater the number, and the larger the size 

 of the upper seams, and the nearer they lie to the seam which 

 is worked at a lower level, the greater the risk of such com- 

 munication by fissures. 



Secondly. The higher beds of coal, which might have been 

 worked to advantage before they were undermined, and when 

 the expense of a shaft had been already incurred, may never 

 be available after th'e workings have been for many years 

 abandoned, and the shaft partially filled up, and after the coal 

 has been injured b}' the continued permeation of water and 

 gas through its fissures, whereby property of great value may 

 be irrecoverably lost to the country. With a view to prevent 

 this prospective evil in the mines belonging to the Duchy of 

 Cornwall in Somersetshire, it has recently been proposed to 

 make provisions in the new leases to secure the more regular 

 extraction of all the workable seams which, exclusive of the 

 great seam, range from 14 inches to 2 feet in thickness, the 

 •whole of them being less considerable than five of the seams 

 neglected in sinking the Haswell shaft. 



