1876.] 275 praes. 



existence of a natural force affecting the material with which their 

 gains are associated, and how the nature of the force determines the 

 method of work. 



Even with this care sudden lateral slippings of the stone have 

 frequently taken place, especially when the channels are nearly com- 

 pleted. These have usually been attended by cracking and explosive 

 sounds, and sometimes the movements have been of such violence as 

 to throw pieces of stone from the surface, or to crush portions of the 

 rock into small fragments. In these instances it has been found that 

 the portion of the bed which has moved has also expanded. The 

 evidences of this expansion are decisive, for the stone permanently 

 retains its enlarged dimensions, and the channel remains very per- 

 ceptibly narrower than it was before. I am informed that there have 

 been instances in which the expanding rock has not only closed the 

 channel, but has also pressed against the stone which was upon the 

 opposite side of the trench with such force that it has been broken. 

 On one occasion the edge of the expanded portion of a bed was ob- 

 served thrust over the other edge, so as to bring one portion vertically 

 above another part of the same bed, which was originally some fifteen 

 inches or more from it horizontally, thus producing, upon a small 

 scale, a reversed fault. Of the lateral movements and expansions of 

 the rock there can be no doubt, and the fact that such phenomena 

 occur whenever like opportunities are presented must be accepted as 

 evidence that the Berea sandstone, like the Monson gneiss, is in a 

 state of lateral compression. 



I found it to be a popular belief at the quarries that the pressure 

 was produced by the weight of the adjacent overlying rock and loose 

 materials, but a careful study of the facts and phenomena will con- 

 vince the intelligent inquirer that the lateral compressions here 

 exhibited could not have been caused by vertical pressure upon ad- 

 jacent parts of the beds. 



It being very desirable to determine whether the lateral pressure is 

 limited in its action to a certain line of direction or not, I have taken 

 special interest in searching for facts bearing upon this question. 

 That the force does act in a northerly and southerly course there can 

 be no doubt, for it is in excavating the east and west trenches, with 

 the northern and southern ends of the beds left undisturbed, that 

 the movements are greatest and most energetic. For an illustrative 

 example, let us consider the conditions of a bed of rock which re- 

 mains undisturbed at the eastern side of the quarry, but which has 



