40 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



Going west across Groshen and Cummiugton, we find the same series 

 repeated and earned still lower, thus: 



4. The upper sericite-schist=Eowe schist. 



5. The horubleude-serpeiitine band^Ghester amphibolite. 



6. The lower sericite-schist=Savoy schist. 



7. The feldspathic mica-schist=Hoosac schist. 



8. The Becket gueiss. 



Now in the Shelburne anticline one passes directly from the coiTugated 

 schists (1) to the gneiss (8), with only the intervention of a single horn- 

 blende band, often not more than 60 feet thick, and this bed thus replaces 

 the Groshen flags and the whole sericite-schist series. 



It is true that the first bed of limestone above the hornblende-schist is 

 white and slightly actinolitie, but it has a border of hard, black hornblende- 

 garnet rock, so characteristic of the limestones of the Conway schist. An 

 insjiection of the map will show that the normal succession of the beds 

 occurs across Shelburne exactly as across the towns north or south of the 

 Shelburne gneiss, from which one is inclined to hesitate between tlu-ee sup- 

 positions: (1) That the Shelburne rocks are the sericite-schist (4 to 6 above) 

 grown feldspathic; (2) that all the beds of the flagstone and sericite-schist 

 series, so abundantly developed just to the west, have thinned out to the east, 

 so that they are represented only by the thin hornblende band; and (3) that 

 the granitoid gneiss is an intrusive rock grown gneissoid by pressure. I 

 am inchned to accept the second supposition, as the hornblende-schist is 

 almost certainly the continuation of the Hawley schist, and one niay assume 

 that the gneisses formed an island larger than the present exposure during 

 the deposition of the sericite-schists and the flagstones. The diminished 

 thickness of these two series east of the Connecticut harmonizes with this 

 assumption. The coloring adopted on the map accords ^Vith this hypothesis. 



Contacts. — Going south along the west side of the river iiito Conway, 

 20 rods north of L. W. and B. A. Andrews's house, one passes for a long 

 distance over a thick-bedded, white biotite-gneiss, and finds this changing, 

 in the hillside west of the road, into a thin-bedded hornblende-biotite-schist 

 with garnets and pyrites. 



The transition is sudden to the hornblende-schist above, and the two 

 rocks are not separated by any fissure, but are welded together intimately. 

 The schist is a thin-bedded hornblende-schist with few garnets, black. 



