25$ PHYSICAL GEOGRAPHY. 



and near to the porch of the cavern delineated, as also in progress towards the other 

 extremity, yawning apertures aloft and laterally communicate with the celebrated ravine 

 in the castle bounds, and receive a blue misty light into the gigantic casemate which 

 illuminates the glistening and sparry walls, displaying the white frosted vapour upon 

 the lips of the attendants and their guide. In sultry weather much danger is incurred 

 by entering the caverns insufficiently protected from an altered temperature. 



The demand for the mineral treasures of the earth, and especially its coal, created by 

 the advance of civilisation, has caused the undermining of its surface upon an extra 

 ordinary scale in modern times, though some of our own mines date their origin from the 

 era of the ancient Britons. This is the case, as the name imports, with Odin's mine, at 

 the southern foot of Mara Tor in Derbyshire, a place deserving a visit. A shaft, nearly 



Entrance to Odin's Mine. 



a mile in length, leads to the vein of ore that is now worked, which varies in thickness 

 from two or three inches to as many feet. Beautiful crystallisations of blende, barytes, 

 calcareous spar, and selenite are found in this extensive excavation, as well as the curious 

 and dangerous mineral called slikensides. " The effects of this extraordinary mineral," 

 says Mr. Rhodes, " are not less singular than terrific. A blow with a hammer, a stroke 

 or a scratch with a miner's pick, are sufficient to rend those rocks asunder with which 

 it is united or embodied. The stroke is immediately succeeded by a crackling noise, 

 which is sometimes accompanied with a sound not unlike the mingled hum of a swarm 

 of bees ; shortly afterwards an explosion follows, so loud and appalling that even the 

 miners, though a hardy race of men and little accustomed to fear, turn pale and tremble 

 at the shock. This dangerous combination of matter must consequently be approached 

 with caution. To avoid the use of the common implements of mining, a small hole is 

 carefully bored, into which a little gunpowder is put and exploded with a match, which 

 gives the workmen time to withdraw to a place of safety, there to await the result of 

 their operations. Sometimes not less than five or six successive explosions ensue at 

 intervals of from two to ten or fifteen minutes ; and occasionally they are so sublimely 

 awful that the earth has been violently shaken to the surface by the concussion, even 

 when the discharge has taken place at the depth of more than one hundred fathoms." 



