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tion. The large proportion of pebbles of elongated shape met 

 with in these beds is, he considered, the natural consequence of 

 the mode of disintegration of the original metamorphic rocks from 

 which the pebbles were derived. Such rocks, in virtue of sharply- 

 intersecting joints and cleavage planes, are prone in many locali- 

 ties to break up in long, irregular, somewhat rhombic figures, 

 which, by the wearing action of streams and tides, are easily con- 

 verted into oblong pebbles like those of the Newport conglomerate. 

 Examples of this mode of disintegration are common in the more 

 altered belts of the Appalachian region, especially among the 

 silicious and argillaceous slates along its southeastern border, and 

 may be seen at various points among the similar altered rocks of 

 New England. 



To the hypothesis of Prof. Hitchcock that these elongated peb- 

 bles owe their peculiar shape and position to the action of power- 

 ful pressure upon the strata while the pebbles were in a soft con- 

 dition from intense heat or other causes. Prof. Rogers urged the 

 following objections. 



1. The effect of pressure upon a plastic solid, as shown by 

 Sorby and Tyndal, is in all cases to develop more or less dis- 

 tinct cleavage planes throughout the mass, these planes being 

 uniformly at right angles to the direction of the pressing force. 

 Such an action, applied on a large scale to the strata of con- 

 glomerate, must therefore have had the effect not only of flatten- 

 ing the plastic pebbles in a uniform direction, but of developing a 

 cleavage or lamination in them all, parallel to their flat sections as 

 they lie in the mass. But this is so far from being the fact, that 

 we find the cleavage planes of different pebbles running in wholly 

 different directions, sometimes across, sometimes parallel, and 

 sometimes oblique to the general bedding, just as might be ex- 

 pected from the preservation of the original cleavage-structure of 

 the rock from which they were derived. 



2. Such a moulding of the pebbles b}^ pressure would either 

 enormously distort or entirely obliterate any fossil forms or im- 

 pressions which may have existed upon or within the pebbles at 

 the time of their deposit. But an inspection of the Lingulce from 

 the Taunton River conglomerate, and of a similar fossil found 

 subsequently by Mr. Easton in the conglomerate of Newport, 



