128 GREEN MOUNTAINS IN MASSACHUSETTS. 



pre-Cambrian or Lower Taconic No. 3 ("talcose slate"), Walcott's Hudson River (Lower 

 Silurian). 



the Berkshire schist (8b). Schist like the Greylock schist, but more frequently cal- 

 careous and plumbaginous, especially toward the underlying limestone (€Ss); thick- 

 ness, 1,000 to 2,000 left. Part of Emmons's pre-Cambrian or Lower Taconic No. 3 

 (" talcose slate"), Walcott's Hudson River (Lower Silurian). 



The Stockbridge limestone (€Ss). Limestone, crystalline, in places a dolomite, 

 quartzose or micaceous, more rarely feldspathic, very rarely fossiliferous. Galena 

 and zinc blende rare. Irregular masses of iron ore (limonite) associated sometimes 

 with manganese ore (pyrolusite). Thickness 1,200 to 1,400 feet. Emmons's pre-Cam- 

 brian or Lower Taconic No. 2 ("Stockbridge limestone"), Walcott's Hudson River 

 (Lower Silurian). 



The Vermont formation (■£?«). Quartzite, cropping out in the Greylock area only 

 once, but probably underlying the entire mass. Thickness, 800 to 900 feet, Emmons's 

 pre-Cambrian or Lower Taconic No. 1 ("granular quartz"), Walcott's " Olenellus" 

 (Lower Cambrian). Total thickness of the series, 5,000 to 7,200 feet. 



The estimates of thickness are based upon the sections. The difference in the 

 estimates arises partly from the varying amount of thickening in plication. The 

 actual thickness is probably less than the minimum figures giveu above, and possibly 

 much less. The maximum thickness of the entire series does not exceed the minimum 

 thickness attributed to the Lower Silurian in the Appalachian region. See page 190 

 for a tabular arrangement of these results. 



Areal geology. — The accompanying geographic map of Greylock and the adja- 

 cent masses presents a great body of the Berkshire schist almost surrounded by 

 the underlying Stockbridge limestone. The Berkshire schist sends out tongues, cor- 

 responding to synclines, into the Stockbridge limestone area. There are also reenter- 

 ing angles of limestone in the schist area, corresponding to anticlines. There are 

 isolated schist areas which are more or less open synclines, and isolated limestone 

 areas which are compressed anticlines protruding through the overlying schist, 

 exposed by erosion. These relations recur between the Bellowspipe limestone (Sbp) 

 and the Greylock phyllite (Sg), but the limestone area southwest of Cheshire appears 

 to be a syncline. 



Relation <>/ ;/<<>/'»/.'/ to topography.— The physically and chemically more resistant 

 schists form the more elevated portions and the steeper slopes, while the broad valleys 

 and gentler undulations about the mountain generally correspond to limestone areas. 

 The limestone and calcareous schist of the Bellowspipe limestone horizon consti- 

 tute the benches of agricultural land high up on the sides of the mountain and the 

 Notch ; and to the presence of this rock also, together with a northerly pitch, is due 

 the deep incision in the central crest between Saddle Ball and Round rock. (See sec- 

 tion Q and PI. xiu and Fig. 74. The north to south part of the Hopper (PI. xvn) 

 is due to the trend and upturned edges of the calcareous belt, and possibly also to 



