DESCRIPTION OF THE GENERAL SECTIONS. 655 



the base station of the mountain railway is a broad expanse of a granitic 

 rock, hke the Concord, not necessarily stratified. Ledges are wanting 

 for about two miles east of the Lower Ammonoosuc falls, where the 

 Conway granite sheets, dipping slightly north-west, appear, constituting 

 the north end of the Rosebrook range. This is the only ledge seen along 

 the river; but the Sugar-Loaves on the southern side consist of similar 

 material. Shortly before arriving at the Twin Mountain house in Carroll 

 are indications of the presence of the typical area of Bethlehem gneiss. 

 The section, unfortunately for showing structure, follows nearly along 

 the line of strike of this formation. The nature of the axes is somewhat 

 uncertain. It seems clearly enough to be an anticlinal, through the 

 diversity of dips near the east end, but synclinal, with a monoclinal in- 

 clination, through Bethlehem. The lower part of the formation is por- 

 phyritic, while the upper is nearly a mica schist, with white feldspathic 

 nodules. The best argument for the basin structure is the occurrence 

 of porphyritic gneiss on both sides, with synclinal dips. 



At Littleton two formations overlie the Bethlehem series, — first, a strip 

 of ordinary (Lake) gneiss, and, second, the Coos schists, the last the most 

 highly inclined. The last are usually between the two gneisses. On the 

 west occurs a narrow strip of the Lisbon group, and then alternations of 

 this with fossiliferous Helderberg (p. 329), The Lyman group comes up 

 west of the Lisbon ; and west of Partridge pond there is a range of clay 

 slate. The section crosses the north end of Gardner's mountain, seen on 

 Plate XIII to consist of several flexures closely crowded together, with an 

 anticlinal in the centre. The clay slate appears in scanty amount west 

 of the Huronian at Barnet. It is inverted beneath the Huronian of Mon- 

 roe, as is also the Calciferous mica schist farther west. No variation in 

 the dip of the latter is noted ; and in the west part of Peacham it comes 

 in contact with the Marshfield area of granite. This eruptive mass is 

 probably of diverse ages, like that of Mt. Ascutney, a part of it being 

 earlier, but most of it later, than the calcareous schists. 



This section was first measured for the Vermont geological survey in 

 1858, and a view of it published in the final report of that state, connect- 

 ing together the White and Green Mountains. The present sketch is 

 not so lengthy ; but the New Hampshire portion has been greatly im- 

 proved over that early delineation. 



