FOLIATION. 



389 



magnetite that the compass is affected by them, even at a distance from the ledges. A 

 surface six feet long and a foot wide, was carefully examined, and several pebbles of 

 granite exhibited upon it, seem to have been elongated since their fixture in the rock. 

 Upon another ledge near by, there were seen also many long and narrow pebbles of slate, 

 which may have been elongated ; but it is difficult to be positive, since it is very natural 

 for slaty rocks to break into long fragments. We have seen no ledges of conglomerate in 

 the State that illustrate the lithological character of a conglomerate so distinctly and 

 beautifully as this. Three large specimens of it in the Cabinet, N"os. ?, ^ and ^5, 

 though excellent, give a very poor idea of the appearance of the ledges. This belt of con- 

 glomerate is about thirty rods wide. 



There are other ledges of. conglomerate between Fairfax and the Canada line ; but they 

 would not attract much attention. The rocks are mostly novaculite schists. 



Divisional Planes. 



We have preserved three observations respecting the position of joints in these talcose conglomerates. 



Locality. Strike. Dip. Observer. 



Richmond, northwest corner, About E. and W., 90, C. H. H. 



Fairfax, center, N. 50 E.\ 39 N., C. H. H. 



Fairfax, east of center, N. 40 W., 25 S.W., C. H. H. 



We have preserved the following observations respecting the position of the laminae of foliation. 



Locality. 

 Fairfax, center, 

 Fairfax, east of center, 

 Fairfax Falls, 

 Westford, north part, 

 Richmond, west corner, 



Strike. 

 N. 38 E., 

 N. 35 E., 

 N.43 



N.23 



'E.,- 

 'E, 



Dip. 

 70 E., 



77 E., 

 80 E., 

 90, 

 50 E., 



Fio. 258. 



Foliation is a term scarcely used yet by American writers. It is a change in metamorphic rocks analo- 

 gous to cleavage. It is a crystalline lamination, or a separation of the different mineralogical compounds 

 into distinct layers, much resembling strata. We suppose that generally. in Vermont the foliation coincides 

 with the stratification. Most observers would call the laminas of foliation cleavage planes. In fact the 

 chief difference between the two classes of planes, is that the former are the result of the same forces as 

 cleavage planes, only they have continued to operate for a longer time, and are not confined to argillaceous 

 rocks. 



Fig. 258 represents the perpendicular face of a ledge in a quarry in the northwest part of Richmond. 

 A jointed plane existed in the ledge, cutting through it, and the workmen have removed all the rock upon 

 the south side of the seam, so that the end of the ledge exhibits its inter- 

 nal structure upon a smooth face about eight feet square. The rock is 

 entirely composed of talcose grit, except a belt of conglomerate, a a, 

 dipping irregularly in the same direction, but at a different angle of 6 

 inclination, from what we have usually called strata, b b, everywhere 

 else. There are no lines of separation between the p'ebbles and the 

 adjoining schists ; they pass into one another insensibly, yet are perfectly 

 distinct. We discovered nothing else in the vicinity similar to this case. 



Similar examples were observed in the north part of Westford. Strata of conglomerate are subdivided 

 by laminte of foliation. A stratum of conglomerate, six inches thick, changes from one kind of material to 

 another in the space of a few feet. It may be compared to a beam of timber, one half of which has been 

 sawed into boards, while the other half is as compact as it was at the first. So this is partly conglomerate, 

 and partly schist. 



