Rogers.] 98 [May 19, 



diameter, and presenting after its changes a series of concentric, loop- 

 like curves, marking surfaces of lamination or partial separation, 

 caused by the relative motions of the different parts. It would seem, 

 therefore, that any flattening and elongation of the pebbles in the 

 conglomerate could not fail to be followed by some analogous altera- 

 tion of structure, and as the pressures or tensions must be conceived 

 to have pervaded the rocks generally, it was to be expected that 

 such induced lamination, or other structure, would be found common 

 to all the pebbles making up the mass. But on careful examination 

 of the principal exposures of the Newport conglomerate, I have met 

 with no evidence of such superinduced structure, although from the 

 fact that the pebbles are for the most part rolled fragments of quartz, 

 quartzite, sandstones and silicious slates, having a more or less jointed 

 or laminated character, an opportunity is frequently presented on the 

 smooth face of the rock for studying their internal structure. 



As an illustration of how independent the lamination and joints of 

 the several fragments are of such hypothetical moulding forces, I 

 have made a tracing of the conglomerate surface, at a particular 

 locality of the Purgatory Rocks, on transparent cloth, which enables 

 me to lay down the actual outlines of the several pebbles with the 

 direction of the laminae in each. In this diagram it may be seen 

 that the lamination has very various directions, and that it extends 

 entirely across the pebbles, leaving no room for supposing even a 

 superficial moulding effect from pressure. The predominant direc- 

 tion of the lamina?, as might be expected, conforms to the general 

 direction of the oblong pebbles, but even in cases where the con- 

 formity is most striking, and the appearance of flattening by pressure 

 most marked, pebbles are interspersed in which the lamination has 

 various transverse directions, sometimes even at right angles to the 

 strike. 



It would seem, therefore, in view of these facts, that there is noth- 

 ing in the structure of the Newport conglomerate to sustain the 

 hypothesis referred to, or to call for further mechanical agency than 

 the transporting and wearing actions under which it is believed such 

 materials have been generally moulded and accumulated, together 

 with the tangential or other pressures, which have been concerned 

 in determining their stratigraphical position. Of the operation of 

 these latter forces there can of course be no question, as the rocky 

 masses of the conglomerate have been forced into steep and alter- 

 nating dips. Moreover,, the cracked and fissured condition, so fre- 

 quent in the larger masses of quartz and quartzite, suggests the 



