406 A. Strahan — Explosive SKckensides. 



throwing the men to the ground, and bruising them considerably ; 

 the thickness of the fragment was equal to the depth of the drill- 

 hole, namely, ten or twelve inches. The toadstone also has been 

 known by Mr. Bowman to break off with a little noise soon after it 

 has been relieved of pressure by excavation. Ecton Mountain is 

 composed of the upper beds of the Carboniferous Limestone, sharply 

 contorted and crushed. 



1 may refer here also to the description by Mr. W. H. Niles,^ of 

 the movements of rocks resulting from lateral pressure, and ex- 

 hibited in quarries. It was found at Monson that the rock has been 

 brought into a compressed condition by a powerful lateral pressure 

 acting in a north and south direction, and that, when opportunity is 

 presented, the compressed rock expands with great energy, often 

 bending, folding, and fracturing the beds, and sometimes producing 

 sudden and violent explosions, and occasionally throwing stones into 

 the air. The expansion became apparent on cutting trenches in the 

 rock in an east and west direction. 



At Lemont, Illinois, the bed of rock forming the floor of a quarry 

 was gradually bent up into the form of an anticlinal, trending east 

 and west, and running for about 800 feet with an elevation of six to 

 eight inches. The elevation had taken place in consequence of the 

 removal of the overlying rock, and had been attended by explosive 

 sounds, and sometimes fragments of the rock had been thrown into 

 the air. In the same quarry it was observed that drill-holes bored 

 through two layers of stone became displaced, the uj)per parts of the 

 holes being no longer vertically over the lower parts. The effects 

 of this force have been noticed at five different localities, ranging 

 over five and a half degrees of longitude. 



Mr. Niles refers also to explosions which have sometimes occurred 

 in making railway-tunnels and other excavations, and which could 

 not be accounted for as the results of any artificial power. 



The tradition among miners that knockings may be heard under- 

 ground, where ore exists, is well known, and has often led to the 

 expenditure of much money. That subterranean noises are not 

 uncommon has been proved beyond doubt, and the following 

 account by a working miner is not without interest.^ 



" I have heard some Miners say that it is a Knocking they hear. 

 Striking much like as when one in Boreing, not constantly but 

 resting by Fits, and always seem to be at a distance 'from him. . . . 

 I once Worked in a Groove not many Years ago, where two more 

 Men wrought, they worked by yards at a deeper Level than I wrought 

 at . . . One day I having some leasure at Work, it struck into my 

 Head to go down to them, . . . but coming there I found no Body, 

 which I did much Wonder at, since I well knew that no Body else 

 wrought within my hearing. Next Day I told the Men how I was 

 mistaken ; see you there says one of them to the other, it is what 



^ The Geological Agency of Lateral Pressure exhibited by certain Movements of 

 Eocks, Proc. Boston Soc. Nat. Hist. vol. xviii. p. 272 (1876) ; see also ib. vol. xiv. 

 and Proc. American Assoc, for the Advancement of Science, vol. viii. p. 285, and 

 vol. xxii. part ii. 



2 The Miner's Dictionary, by "William Hooson, 8vo. Wrexham, 1747 (under the 

 head Knocker). 



