302 



their origin may be called dynamic breccias^ and those which 

 resemble ordinary conglomerates may be called pseudo- 

 aonglomerates." 



In an earlier work, ''On Some Dynamic Phenomena," ('^^ 

 Van Hise had already used the term '^friction-conglomerate^' 

 for similar phenomena. Under the heading, "Some Dynamic 

 Phenomena shown by the Baraboo Quartzite Ranges of Central 

 Wisconsin," he says, ''For the most part the rock is merely 

 fractured, the quartz fragments roughly fitting one another, 

 but there are all gradations from this phase to a belt, about 

 ten feet wide, of true friction-conglomerate, the fragments 

 having been ground against one another until they have 

 become well-rounded (a Heibungs breccia). Between the 

 boulders of this zone is a matrix composed mainly of smaller 

 quartzite fragments." 



Another interesting observation, of a like kind, was made 

 by Van Hise in the Pre-Cambrian rocks of the Adirondacks 

 Mountains. He says, "In the Adirondacks is a thick forma- 

 tion of gneiss overlain by a bed of crystalline limestone 

 containing interlaminated smaller beds of gneiss. The whole 

 series has been closely folded. The gneiss, as a result of the 

 folding, is closely corrugated, and to a certain extent its 

 iipper folds are truncated by the shearing action. The lime- 

 stone has acted like a fluidal substance, accommodating itself 

 easily to the new position, and by re-crystallization has taken, 

 on a massive character. The thin beds of gneiss within the 

 limestone have been broken to fragments. The fragments 

 within the limestone matrix have ground against one another 

 until they became well rounded. They are disseminated 

 through the limestone. As the layers of gneiss are thicker 

 and more numerous near the base of the limestone, this part 

 of the formation appears as a limestone containing numerous 

 boulders and smaller fragments of gneiss resting upon a gneiss 

 formation. "(5) The resemblance which such a geological 

 section bears to a basal conglomerate with derived fragments 

 from an older rock along a plane of unconformability is so 

 close, that it cannot be wondered at that in the first instance 

 the section was so interpreted. The true nature of the section 

 was discerned when it was noticed that the conglomerate 

 could be traced along the line of bedding to where it could 

 be seen that the gneiss was interstratified with the limestone. 



An important paper was read by Mr. G. W. Lamplugh 

 before the Geological Society of London in 1895, on "The 



(4) Jour, of Geology, vol. i., 1893, p. 351. 



(5) Van Hise, ''Deformation of Rocks," Jour, of Geology, 

 vol iv. (1896), pp. 628, 629. 



