270 Dale — Oatiihn'nn Conglomerate of Ri.pton in Vermont. 



Middlohnrv River 1/2 mile M'ost of Kiptoii vil]ni>'e, wliicli, 

 jiul«;iiii>' from its ivlation to otlier outcrops on the hillside south, 

 probably measures about 500 ft. from east to west and 1500 ft. 

 from north to south, tapering out at the north. Some parts of 

 this blue quartz are schistose, but a thin section of that shows 

 no feldspar but a matrix of sericite carrying large particles of 

 quartz containing a few biotite scales. If the sericite is altered 



Fig. 3. 



Fig. 3. Beach pebble of blue quartz of pre-Cambrian origin in schist 

 and conglomerate of Lower Cambrian age near Chandler house in Eipton, 

 Vt. Size 76 x 57 x 80 inches. Sledge and bag rest on conglomerate. In 

 distance central range of Green Mountains. 



feldspar, then we have to do with a very acidic granite-gneiss, 

 but most of the blue quartz i-ock is probably of pegmatitie 

 origin. Fine-grained quartz monzonite crops out at points 

 1 1/4 miles west and 1 3/4 miles N.E. of Ripton village. 



Conclusion: The generally rounded or discoid foi-m and the 

 unstriated surfaces of these pebbles from the Cambrian con- 

 glomerate point to their having been formed on a beach, and 

 their magnitude points to their local origin, which is corrobo- 

 rated by the occurrence of identical gneisses, quartz monzonite 

 and blue quartz in the underlying or adjacent pre-Cambrian. 

 The quartzite pebbles show the existence of Algonkian sedi- 

 mentary rocks on the Green Mountain range. These large 

 beach pebbles thus take us back to the time of the Cambrian 

 sea as it advanced over the very slowly subsiding pre-Cambrian 

 land-mass of central Vermont. 



Pittsfield, Mass., June 21, 1910. 



