356 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



thick, containing many smaller pebbles of the white vein quartz in a deep- 

 red paste. This graduates into a deep chocolate-coloi-ed layer — a coarse, 

 pebbly arkose — full of musco\ate and feldspar, but with much vein quartz, 

 and argillite also, and this continues upward across the brook, becoming 

 lighter in color. 



Entering the gorge of the next tributary, 50 feet lower down on the 

 same side, one finds that the brook has just cut down to the argillite, but 

 traces of the basal conglomerate bed can be found resting nearly horizon- 

 tally on the vertical slates for 245 feet up the brook. It is a striking rock, 

 from the large white quartz pebbles in the bright-red sand. Above this, 

 just at the entrance of the brook, is a fine bluff, and in it the basal bed 

 grades tlu-ough 3J feet of fine red sandstone into a bed, 10 feet thick, 

 of coarse buff arkose with two thin conglomerate layers, and above this 

 is a bed, 10 to 12 feet thick, of a coarse conglomerate with pebbles an 

 inch across; strike N. 70° E., dip 15° S. These are mostly well-rounded 

 masses of the vein quartz from the argillite, also of gneiss, mica-schist, 

 argillite, etc. These bowlders are often full of iron rust, a fact which 

 may throw light upon the penetration of biotite into all the pebbles of the 

 Cambrian gneisses of Berkshire. We see that the circumstances favoring 

 the deposition of iron rust were present from the beginning, and that after 

 a brief period (during which the waters advancing upon this sharp slope 

 deposited only the angular quartz masses so generally abundant in the 

 argillite, yet wanting just here, but which were transported only a little 

 Avay) tlie strong tidal currents brought up from the south the granitic mate- 

 rial of the Williamsburg area, and that there for a long time and for a con- 

 siderable distance out into the valley by far the larger and the finer portion 

 of the deposit .was this far-traveled granite debris, while the coarser and 

 more angular portion was vein quartz from the argillite. The black mud 

 from the latter seems to have been swept away entirely and to have found 

 no place of permanent deposit north of Holyoke. 



The shore conglomerates are concealed by the Green River lake-beds 

 south across Greenfield and the north of Deerfield, but opposite Pine Hill 

 and the north part of Deerfield village the brooks coming down from the 

 west cut through the heavy sands of the high terrace and expose the Tri- 

 assic beds nearl}- up to the conglomerates, especially in the brook south of 

 J. F. Hartwell's and in the roadside running down into the valley near the 

 Baptist church. 



