2/4 STRATIGRAPIIICAL GEOLOGY. 



of Littleton, Whitefield, Bethlehem, and Dalton, forming an oval-shaped 

 isolated area of about four square miles in extent. The Ammonoosuc 

 flows along its eastern border ; and there is a large hill in the western or 

 central part, about six hundred feet above the river. This area is the 

 most northern exposure of the porphyritic gneiss in the state. It is sup- 

 posed to be connected with the great Lafayette-Moosilauke range be- 

 neath the overlying Bethlehem group, and to be the oldest formation in 

 New Hampshire. 



The determination of the dip of this rock near the Wing Road station 

 has been a difficult matter. There are jointed planes, with scarcely any 

 inclination that might be taken for strata. At the suggestion of Dr. T. 

 Sterry Hunt, a crystalline arrangement of materials dipping 75° S. 40° 

 E. was decided upon to represent the strata. The first set of nearly hor- 

 izontal divisional planes presented no variation of mineral composition, 

 but the second exhibit an alternation of coarse gneisses, fine feldspathic 

 layers, and other varieties, separable only by a difference of character. 

 They are also more irregular than the others. The gneisses show two 

 feldspars, — orthoclase and oligoclase, — two micas, — muscovite and bio- 

 tite, — and amorphous quartz. On the north town line of Bethlehem, and 

 at the west base of Kimball hill, I found a ledge of the rock having in it 

 a gneissic seam, two inches thick, dipping 25° N. 20° W. The hill west 

 of the Ammonoosuc, sometimes called Bald hill, is composed of a bare 

 ledge of this rock. It is most conspicuous as seen from the village of 

 Bethlehem, and is a spur of Mann's hill, with but a slight valley between. 

 The feldspar crystals are conspicuous on Mann's hill, near the junction 

 with the mica schist, and the dip is about vertical, perhaps 70° N. 75° 

 W. It is presumed this rock outcrops in the south-east corner of Dalton. 



The south-western mnd of the most imj^ortant area of Bethlehem gneiss 

 projects into the Ammonoosuc field, crossing the river just above North 

 Lisbon. The dip is unusually low on the river, being only 30° northerly. 

 At the "lead mine" the dip is 36° north-west. Farther to the north-east 

 the dip rises to 75°. As the strata are monoclinal, from an inversion, it 

 is difficult to determine whether the axis is anticlinal or synclinal, with- 

 out reference to other parts of the terrane. It would seem to be an over- 

 turned synclinal, when all parts of the terrane have been compared with 

 each other and the adjacent formations. The angle of inclination is less 



