662 STRATIGRAPHICAL GEOLOGY. 



Various well ascertained sections will be mentioned, from which our 

 column may be constructed. 



In various parts of the Connecticut valley are narrow but persistent 

 bands of hornblende schist, usually skirting the borders of gneiss. Near 

 the west ends of Sections I and II in Vermont this band is seen unequiv- 

 ocally to fold over an arch of gneiss. The same feature is shown even 

 more palpably at Shelburne falls, Mass., where the same four groups 

 appear successively on both sides, viz., — gneiss at the base, dipping 15 or 

 20 degrees; hornblende schist, mica schist, and Calciferous mica schist. 

 There is a similar strip along the eastern border of the gneiss between 

 Athens and Hartland, Vt.; and the underlying rock has the anticlinal 

 structure, shown from careful scrutiny upon Section V. The same belt 

 of rock lies above the Hanover gneiss, the Westmoreland area, and others, 

 with the same relative positions. The Vernon-Hinsdale gneissic area is 

 likewise encircled by this rock, but the dip is monoclinal : hence we have 

 here an example of an inversion whose genuineness cannot be called in 

 question. The hornblende layer occurs in a few other localities where 

 our information is scanty ; but the facts warrant us in assuming the ex- 

 istence of the same relations in the unknown as well as in the familiar 

 spots. 



The position of the porphyritic gneiss may be gathered from two or 

 three classes of facts. The most extensive range, between Groton and 

 Jaffrey, is flanked by the Lake and Montalban groups for a large share 

 of its development. Going east from Warner, the Lake gneiss is well 

 marked in Webster, followed by Montalban schist in Boscawen. Going 

 south-west from the same town, after a long journey to cross the group, 

 the Lake gneiss is first seen, extending all the way from Grafton to mid- 

 dle Stoddard in immediate proximity; and next is the Montalban from 

 Stoddard to the state line south. The topographical distribution of these 

 three formations indicates very clearly a succession. From what has 

 been stated, either the basin or ridge structure is needed to explain the 

 recurrence of identical formations on both sides of the porphyritic gneiss, 

 which, by the way, is located along the height of land between the Con- 

 necticut and Merrimack rivers. Now the porphyritic gneiss possesses 

 the fan-shaped disposition of strata; and there is very commonly a dip 

 of the Lake gneisses towards it, both from the east and the west, as if 



