HAWKINS, LOCKATOSG FORMATION OF THE TRIASSIC 167 



taken place in a horizontal direction, being in the nature of a shove or 

 heave without much deviation from horizontality. Such movement has 

 been quite general throughout much of the formation. It appears to have 

 been the result of a tension which opened each crack with a twisting mo- 

 tion, often bending strips of one wall across the cavity without breaking. 

 This is much like the phenomenon which Dale^^ observed in Vermont, 

 and which he described in the Sixteenth Annual Eeport of the United 

 States Geological Survey. In some cases, as shown by the Princeton ex- 

 posures, the movement tore strips completely away from the rock walls, 

 and in others, crushed sections which were weak or exposed, forming tri- 

 angular areas of intense brecciation at points of intersection with the 

 older joint series which it crosses. The sharp brecciation would indicate 

 that the movement took place suddenly, after the rock had become thor- 

 oughly hardened, and within a distance of the ground surface not too 

 great to allow the rocks to be within the zone of fracture. Probably the 

 load above was relatively small. The angular fragments of argillites in 

 the breccias appear to be perfectly fresh and unaltered, even at the very 

 margins, when examined macroscopically or microscopically. The min- 

 erals surrounding the fragments, the earliest and most important of 

 which were ilmenite, brookite and analcite, must therefore have been 

 introduced soon after the formation of the breccia. 



In some portions of the breccia, the fragments of rock appear to be 

 some distance apart from each other, many at first appearing as if they 

 might be entirely free from any point of contact with other breccia frag- 

 ments or with the walls of the fissure; that is, they appear to be sus- 

 pended in the vein filling. A systematic study of favorable portions of 

 the breccia, by observation of successive surfaces of a specimen ground 

 down on a lap, shows that the fragments are very irregular, and that each 

 rests against its neighbor at one or more points. This helps to show that 

 the solutions from which the minerals were deposited came in slowly, 

 while from them the minerals here found gradually crystallized. Francis 

 H. Butler,^^ in October, 1911, published an account of an investigation 

 of brecciated material, wherein somewhat similar methods were described. 

 Attention is especially called to Plate V, accompanying i\Ir. Butler's 

 paper. The breccias which he has chosen, especially in Figures 12-15, are 

 identical in appearance with some of those from Princeton. 



The. major joint series, as developed near Princeton, is very persistent 

 in strength and direction, being always approximately north forty de- 



21 "Structural details of the Green Mountain region," U. S. Geol. Surv. 16th Ann. Rept., 

 p. 15. 1894-1895. 



33 "The brecciation of mineral veins." Min. Mag., Vol. XVI, No. 74, October, 1911. 



