4l6 THE JOURNAL OF GEOLOGY. 



in grouping of the component minerals rather than to differences 

 of composition. Gneisses are most common, occurring as fine- 

 grained, chloritic rocks or coarse biotite, augen-gneisses. A 

 brownish coarse gneiss with porphyritic crystals of orthoclase 

 extends in intermittent outcrops from Wilcox Hill on the north 

 to Button Hill on the south, a distance of eight miles. This 

 rock carries both biotite and muscovite, the latter evidently 

 derived from the feldspar. In Eastham, Northam, and east of 

 Bear Mountain, there are areas of coarse biotite gneiss with inter- 

 stratified beds of quartzite and limestone. Fine-grained, chloritic 

 schists and gneisses are abundant, as on the summit of Saltash 

 Mountain. 



The area immediately about Mount Holly village on the 

 Central Vermont Railroad, is characterized by a great number 

 of amphibolites. These occur as schists, either intrusive or 

 extrusive, and as dikes, cutting one another, and the country 

 rock. They occur interlaminated with various rocks — quartzites, 

 gneisses and schists, and possess the local schistosity of the 

 enclosing rock. This is as true of the dikes as of the sills, afford- 

 ing a conception of how far removed from any key to the real 

 stratification is the lamination of these rocks and how faulty 

 geological interpretation must be when deciphered on the basis of 

 induced structures. Aside from the interest one naturally feels 

 in eruptives as old as these, their importance as evidence in 

 separating the Mendon from the Mount Holly series cannot be 

 overestimated. Modern basic dikes of camptonite and other 

 igneous rocks traverse the core rocks, but they are younger than 

 the last disturbance of the Green Mountains, cutting Algonkian 

 and Cambrian rocks alike. 



Following the accepted definition of the Algonkian rocks, 

 this lower series as well as the upper must be grouped as Algon- 

 kian. Although possessing many rocks undoubtedly igneous, 

 and others whose origin is problematical, there is a considerable 

 development of genuine sedimentary rocks, warranting us to 

 place the whole series among the Algonkian. The evidence for 

 this sub-division, which is based upon manifold differences between 



