1875.] 413 [Dodge. 



At Punkapog Village, south of Punkapog River, there is some 

 large conglomerate on each side of Washington Street very like that 

 north of the Blue Hills in towns near Boston. About two miles 

 west-south-west, there is a very interesting section exposed by a cut- 

 ting of the Boston and Providence Railroad. This, in fact, affords 

 almost the only opportunity of getting more than the most superfi- 

 cial acquaintance with the strata of this region. The track passes 

 through a hill capped with much gravel which rests on a ridge of 

 various strata dipping 45° N. and with a strike of about E. N. E. 

 Their order from the top southward is, 



Schists, 5 feet thick. 



Sandstone, 7 feet thick 



Quartz, 3 " " 



Schist, 25% " " 



Red schist, 49 " " 



Sandstone, 14 " " 



Quartz vein, 2 " " 



Schist, 11 " " 



Limestone, 2 " " 



Sandstone, 64 " " 



Schist, IVz u " 





Total, 190 feet. 



The sandstone is very crystalline in appearance. The schists are in- 

 variably red and ferruginous. The quartz veins have a southerly dip 

 and are massive and milky, sometimes varying to transparent green, 

 and again reddish. The limestone is white, but becomes impure 

 when it merges into the schists with which it is interstratified. It is 

 somewhat contorted, although the other strata show no such appear- 

 ance. The philosophy of the association of these strata seems to be 

 that by the decomposition of felspar (which consists of silica and 

 alumina with lime or soda and often ferrous oxyd), and hornblende 

 (which is composed of silica, magnesia and lime or ferrous oxyd), 

 and other minerals, the materials are accumulated in whose quiet 

 sedimentation, the mechanical deposition of the less finely divided 

 gravels and sands alternates with that of iron particles and the pre- 

 cipitation of lime. 



Passing farther in the same direction, there is an island of con- 

 glomerates in the Neponset meadows on the west side of the river, 

 with a dip 45° N.; other outcrops a mile farther on, east of the river; 

 and across it, along its southern bank until it is again reached higher 

 up, on the western side of the loop it here makes around the last 

 named ledges. Across the river again, south-west of the last, a little 

 farther than it from the crystallines to the north, the conglomerates 

 appear again on both sides of Centre Street, the straight road to 

 South Walpole, extending south-westerly as a ridge of red sandstone 



