PLASTICITY. 31 



observer that the materials must have been in a soft state when they were produced. 

 There is no evidence that the opposite walls have slid upon one another at all, as the 

 opposite parts of the pebbles coincide. It seems as if a huge saw or cleaver had done the 

 work. 



These proofs of plasticity apply essentially though less forcibly to the micaceous and 

 talcose cement which has also been cut-across by the joints. Though generally in small 

 quantity, it sometimes forms layers of considerable thickness, interstratified with the 

 pebbles. 



Some have imagined that the elongated, flattened, bent, and indented pebbles of this 

 conglomerate may have been worn into their present shape, and brought into a parallel 

 arrangement, by the mechanical attrition of waves and currents. We feel confident that 

 extensive and careful examination of the localities, and of beaches where shingle is now 

 being formed, will conA r ince any one that they cannot have had such an origin. 1. We 

 do not believe that any beach can be found with pebbles that have anything more than 

 a slight resemblance to those at Newport. Those somewhat elongated may indeed be 

 found, when they are derived from slate rocks. But nowhere does the attrition of pebbles 

 against one another produce deep indentations and leave the one neatly fitting into the 

 other, nay, one bent partially around the other, as is the case at Newport. If these 

 phenomena were produced by original attrition, how strange that they should have such 

 an extraordinary development in Rhode Island, while it is not marked enough in any 

 other conglomerate in our country, so far as I know, save in Vermont, to have arrest- 

 ed the attention of geologists. 2. The remarkable joints in this conglomerate prove that 

 the pebbles have been in a plastic state, and since the strata have been much folded and 

 consequently subjected to strong lateral pressure, how could the pebbles have escaped 

 compression and modification of form ? A mass of the conglomerate, when broken open 

 along the line of strike, a good deal resembles a pile of tobacco, which has been rolled 

 into lumps and then subjected to strong pressure, so that the junks are distorted and 

 made to conform to all the irregularities around them. 



3. The force by which the pebbles were flattened and indented must have operated 

 laterally, as would be done by the plication of the strata, folds in which are frequent. 

 And if there was a great superincumbent pressure, and less in the direction of the 

 strike, the same lateral force might have elongated the pebbles. But perhaps there may 

 have been, also, a horizontal curvature in the strata to aid in the work, as we shall 

 explain when Ave come to describe the Vermont localities. It may not, however, be easy 

 to show how this compressing force has operated where rocks have been so folded and 

 disturbed as around Newport, for the conglomerate is in juxtaposition with granite, 

 which has exerted a powerful metamorphic influence on other strata there ; but if we can 

 show the results of the agency, our main object will be accomplished. 



4. The phenomena of the joints in this rock conduct us most naturally to some polar 

 force as the chief agent in their production, such as heat or galvanism. Mere shrinkage 

 could not have separated the pebbles so smoothly ; much less could a strain from beneath 

 have thus fractured them, for sometimes the joints are not more than two or three inches 

 apart ; and if we suppose one of them to have been the result of fracture, yet how is the 

 other to be obtained in that manner ? A simple inspection of the rock in place will 



