Mies.] 272 [April 5, 



April 5, 1876. 



The President, Mr. T. T. Bouve, in the chair. Thirty-one 

 persons present. 



The following paper was read : — 



The Geological Agency of Lateral Pressure exhibited 



BY CERTAIN MOVEMENTS OF ROCKS. By W. H. NlLES. 



Probably no form of geological power has been more efficient in 

 the formation of the fundamental features of the earth than the 

 lateral pressure occasioned by the contraction of the globe. That 

 the strata, yielding to this force, have been flexed and folded, and 

 that by its action mountain chains and continents have received 

 their elevation, is now a commonly entertained belief. While nu- 

 merous well observed facts corroborate the opinion, that lateral 

 pressure must have been one of the most constant and efficient geo- 

 logical agencies of the past, few have enjoyed opportunities for calmly 

 witnessing its operations, or for quietly studying the processes of its 

 action. 



It is the object of this article to consider the evidences of the 

 present activity of this power which are disclosed at certain local- 

 ities by movements of rock and associated phenomena. For a 

 partial description of these evidences the reader is referred to a 

 preliminary paper upon " Some interesting Phenomena observed in 

 Quarrying," published in the Proceedings of the Boston Society of 

 Natural History, Vol. XIV. A further explanation of the charac- 

 teristics of the force manifested has been given in a paper " On some 

 Expansions, Movements and Fractures of Rocks, observed at Mon- 

 son, Mass.," and published in the Proceedings of the American 

 Association for the Advancement of Science, Vol. XXII, Part 2. 



The observations recorded in these papers were considered as 

 establishing the following conclusions respecting the rock at Monson: 

 1. That it has been brought into a compressed condition, by a pow- 

 erful lateral pressure acting only in a northerly and southerly 

 direction ; 2. 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, 

 rending and displacing the rock, and occasionally throwing stones 

 and other debris into the air. Whether these phenomena were to be 



