498 QUARTZ ROCK. 



lower Silurian. But this is a most difficult subject, and the end is not yet. Our chief 

 aim has been to present the facts without bias. We may have mistaken them, some- 

 times, but it has not been through the influence of any hypothesis, if we know ourselves. 



The map will show that as the two easterly bands of clay slate approach the southern 

 part of the State, they almost disappear and are replaced by more crystalline rocks, such 

 as gneiss and hornblende and mica schist, with outbursts of syenite and granite. Our 

 belief is that the metamorphism has been more intense in such places, and has converted 

 the slate into the other rocks. In another place we shall endeavor to show that very 

 much of the granite and syenite along the Connecticut valley has been formed by the 

 melting down of conglomerate schists and slates. We have alluded already to a case 

 where the slate, in the northeasterly part of the State, seems to abut against the granite. 

 So in the southern part we find dikes of granite in the slate which have in them frag- 

 ments of slate. 



QUARTZ ROCK. 



This rock has been so fully described under the fossiliferous group that it is hardly 

 necessary to notice it again. The only reason for doing so is, that east of the mountains 

 we have found in it no fossils. Yet, in the southeast corner of the State, or rather just 

 within the limits of Massachusetts, at Bernardston, it is most distinctly and conformably 

 superimposed upon limestone not older than the Devonian, as we have shown under clay 

 slate. This deposit in Vernon has no great thickness, though greater in Bernardston. 

 So in all other places east of the mountains, the beds of quartz are generally but a few 

 feet thick. They are interstratified with talcose schist and gneiss, as indeed the quartz is 

 on the west side of the mountains. Generally the quartz in these more crystalline rocks 

 seems to have undergone a more thorough metamorphosis, so as to become frequently 

 hyaline. The white tubercular masses of quartz not uncommon in clay slate and mica 

 schist, seem to have been for some reason more free from iron than the granular and 

 more colored varieties west of the mountains. But this subject has already been treated 

 of under metamorphism and elsewhere. 



The geological associations of many of the beds of azoic quartz may be seen upon our 

 sections, though we have attempted no distinction between the fossiliferous and azoic 

 varieties. The lithological characters of all the varieties can be learnt only by consulting 

 the specimens in the State Cabinet. In this place we propose only to present our views 

 of the geological position, equivalency and origin of all the quartz rock of the State. We 

 first give, however, a list of the dips and strikes of quartz rock in Vernon, Bernardston, 

 and Plymouth. 



DIP AND STKIKE OF QUAKTZ ROCK OF TWO RANGES IN EASTERN VERMONT. 



[The locality, strike and dip, and initials of the Observer are given.] 



North Vernon, strike N. 14 E., dip 25 E., C. H. H. North Vernon, strike N. 10 E., dip 30-35 E., C. H. H. 

 Vernou, north of hotel, strike N. 10 E., dip 40 E., C. H. H. Vernon, glass sand locality, strike N. 10 W., dip 40 E., 

 A. D. H. and C. H. H. Vernon, southwest part, strike N. 30 E., dip 70 E., C. H. H. Vernon, southeast part, strike 

 N. 60 E., dip 35 S.E., C. H. H. Northfield, Mass., near Vermont line, dip 30 E., C. H. H. Bernardston, Mass., 

 east part, strike N. 55 E., dip 10-12 E., C. H. H. Bernardston, near the limestone, strike N. 65 E., dip 29 E., 



