486 G. L. VOSE ON THE DISTORTION 



dom over the one hundredth of an inch in diameter, which under the microscope are seen to 

 be composed of many lamina}, which when they lie parallel to the cleavage planes, are undis- 

 turbed, but when perpendicular to those planes, are distorted and bent ; and he further 

 states that calc-crystals, filling the cavities of organic bodies in uncleaved limestones, have 

 their crystalline cleavage planes almost invariably straight, while in a highly cleaved speci- 

 men, the calc-spar is bent and crushed ; showing, as he remarks, that the compressing force 

 acted so intensely and so gradually, as to change the molecular arrangement even of calc- 

 spar, and bend it. 



It is hard to understand how a portion of the pebbles could have been so very much 

 distorted, as we see them, while others nearly adjacent should have been altered but little, 

 or none at all. We often find in these conglomerates schistose pebbles, with the lamina? at 

 right-angles with the general plane of the flattening. This has been considered as evidence 

 against the idea that a compressive force has flattened the pebbles ; as it is said that such a 

 force would develop a lamination in these slaty pebbles parallel with, but not perpendicular 

 to, the general flattening. PI. XVIII, fig. 2, may be considered as an answer to this objec- 

 tion, for the bending and indenting of the upper pebbles is too plain to leave any doubt as 

 to the direction of the force ; it is equally plain that such a force could not have produced 

 the lamination shown in the lower pebbles, which must therefore be regarded simply as the 

 original schistosity of the rock from which those pebbles were made. 



In some cases, the form of the pebbles has been altered without any change in the mineral 

 character ; and in other instances the mineral nature seems to have been entirely altered, 

 while the form of the pebble remains unchanged. Possibly where the cement is deficient, 

 so that the pebbles are at once brought in contact, the change of form will take place, and 

 the force, relieving itself in such a manner, will not produce a metamorphosing heat, 

 while, when the cement is abundant, a heat will be developed in the mass before the pebble* 

 are brought together, and mineral changes will result, without so marked a distortion of the 

 pebbles. If we should fill a strong iron box with leaden bullets, and fit a plunger into the 

 top of the box, and force it down sufficiently, we should distort the bullets, which would 

 become flattened at the points of contact, until the interstices were filled up ; and so long 

 as the force was allowed to relieve itself in this manner, we might have no great heat 

 developed ; but if we placed a few bullets, at a distance from each other, in a box of sand, 

 and compressed the sand, the force would be applied to the bullets in a sort of hydrostatic 

 way, and would not tend to distort them, but would, after the sand was somewhat consoli- 

 dated, apply itself to the production of a heat sufficient to alter the whole mass mineralog- 

 ically. The analogy is, to be sure, not very close between the natural and the artificial pro- 

 cess ; but as the pebbles are generally harder than the cement, certainly so in the early stages 

 of the conglomerate, it may have some value. If the conglomerate was compressed while 

 the cement was still in an incoherent state, of course the matrix would be affected much more 

 than the pebbles; but if the strata were not folded up until the whole mass was rigid, 

 the pebbles and the cement would have to bear the compression more equally. 



It has been remarked, that certain granitic rocks have been produced by the metamor- 

 phosis of conglomerates. The Kangely conglomerate has in some cases certainly been con- 

 verted into a homogeneous crystalline mass, resembling syenite ; and we believe that a 

 severe compression continued for a long time will account for all of the various phenomena 

 seen at the above-named place. The conglomerate certainly commenced as an incoherent 



