4/2 STRATIGRAPHICAL GEOLOGY. 



it extends northward through Nelson, and in the north part of the town 

 it outcrops near M. Wilson's. It then extends north through the central 

 part of Stoddard, thence into Washington, and probably dips under the 

 common gneiss, to come up again in the narrow Marlow range. In the 

 east part of Stoddard, as well as in the east part of Washington, there 

 are not only numerous ledges of porphyritic gneiss, but in many places 

 there are boulders of immense size. In the study of this rock we have 

 found in Ellsworth that there are areas of it surrounded by fibrolite 

 schist, and that on the east it is unconformable with the schist ; that in 

 Orange, the relation of the two rocks are not certain, as they do not 

 come in contact; that in Sunapee, we have detached masses, on both 

 sides of which are micaceous and granitic gneisses of White Mountain 

 series, — and the same fact has been observed in Fitzwilliam ; that in 

 Marlow, it has, on the south and south-east, gneisses that cannot be re- 

 ferred to either of the well-marked divisions of the rocks; that in Ches- 

 terfield and Winchester, it has at least on one side the common gneiss ; 

 and that in Jaffrey, Dublin, Nelson, and Stoddard, it is associated with 

 a siliceous pyritiferous schist, that is found not unfrequently in basins 

 of the porphyritic gneiss. The fact that rounded fragments of a dark 

 gneiss are found in the porphyritic shows that the porphyritic rock in 

 Fitzwilliam is either intrusive, or that in the process of metamorphism 

 these fragments were not obliterated, and that the dark gneiss — which 

 is very limited, but resembles some varieties of the Bethlehem gneiss — 

 is the older rock. 



The Bethlehem or Protogene Gneiss, and the Common or Lake 



Gneiss. 



The common gneiss enters this topographical district from the north, 

 and its western limit coincides very nearly with the western boundary of 

 the Atlantic or gneissic period, as represented on a map in Vol. I, opposite 

 page 516. It extends a little more to the west in Westmoreland; and 

 although in Hinsdale the rock is a gneiss, it does not seem to be the 

 common variety ; and, as already noted, the rock from Chesterfield south- 

 ward is porphyritic gneiss. The eastern boundary is for the most part 

 definite and easily traced, and the rock bordering on it is a fibrolite schist. 

 It extends southward through the cast part of Landaff, through Benton 



