284 ANNUAL OF SCIENTIFIC DISCOVERY. 



pebbles were derived. Such rocks, in virtue of sharply-intersecting joints 

 and cleavage planes, are prone in many localities to break up in long, 

 irregular, somewhat rhombic figures, which, by the wearing action of 

 streams and tides, are easily converted 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 siliceous 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 pebbles owe 

 their peculiar shape and position to the action of powerful pressure upon 

 the strata while the pebbles were in a soft condition, from intense heat or 

 other causes, Prof. Rogers urged the following objections : 



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

 Sorby, is in all cases to develop more or less distinct 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 conglomerate must, therefore, have had the effect not only of 

 flattening 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, some- 

 times across, sometimes parallel, and sometimes oblique, to the general 

 bedding, just as might be expected from the preservation of the original 

 cleavage-structure of the rock from which they were derived. 



2d. Such a moulding of the pebbles by pressure would either enormously 

 distort or entirely obliterate any fossil forms or impressions which may 

 have existed upon or within the pebbles at the time of their deposit. But 

 an inspection of the Lingulte from the Taunton River conglomerate, and 

 of a similar fossil found subsequently by Mr. Easton in the conglomerate of 

 Newport, shows that no such violence could possibly have operated on the 

 mass. 



3d. While in the localities referred to the majority of the pebbles have the 

 oblong shape and parallel arrangement above described, there are many 

 scattered through the mass which are either round or have their longer 

 dimensions more or less transverse, or even perpendicular, to the general 

 direction. As these could not have escaped the enormous, all-pervading 

 softening action and pressure which the hypothesis assumes, their presence 

 in these discordant conditions seems of itself a sufficient refutation of the 

 theory. 



In regard to the curved form and close adaptation observed in some of 

 the pebbles, Prof. Rogers thought that accidental peculiarities of shape in 

 the original fragment, and the effects of attrition and the close packing of 

 the accumulated deposit, furnished an adequate explanation both of the bent 

 form sometimes met with, and the accurate fitting of the contiguous pebble 

 to its concave surface. 



As an example of the formation of flattened pebbles by the action of the 

 shore waves, Prof. Rogers referred to paving stones of slaty trap, recently 

 imported from Newfoundland, which are remarkable for their very uni- 

 form circular outline, their smooth, slightly convex faces, and a thick- 

 ness rarely exceeding one-third of their breadth. If we suppose a great 

 nuiss of these as they lie piled along the shore, with their broad sides 



