528 GEOLOGY OF OLD HAMPSHIEE COUNTY, MASS. 



I hardly need call attention to the magnitude and the peculiar char- 

 acter of the force which has done this work, grinding down all the pebbles 

 of a conglomerate, hard and soft alike, to a common level, as can be well 

 seen on the road which goes over tlie north shoulder of Mount Toby just 

 after leaving the Sunderland road, and cutting grooves in the trap, a rock 

 so tough that one rarely attempts to drill a hole in it, preferring, when it 

 is necessary to remove it, to do the work by building fires upon it and 

 drenching the rock with water, by which means it is crumbled and slowly 

 removed. Two men and a holder drill only 8 feet a day in trap. These 

 grooves are of all dimensions, ranging from fine lines, visible only in 

 oblique light Avith a lens, to broad troughs. 



Even more striking is the polishing of the surface of the great emery 

 vein in Chester, which for a distance of several rods near the summit of each 

 mountain has been deeply grooved and polished by glacial action. That 

 the friction producing this effect must have been enormous is apparent from 

 the size and depth of the channels, and that it could not have been the 

 result of running water is demonstrated by recurring to the example of 

 river action in the Westfield River upon another i)ortiou of the same bed, 

 where we have an eroded, pitted surface from which the coarse crystalline 

 particles of the hard emery are left projecting.^ 



Another point deserving, perhaps, further consideration here is the 

 great degi'ee of irregularity in the direction of the strije, since these give 

 accurately the direction of the motion of the ice at the time they were 

 made. For many of these differences of direction we may assume, as above, 

 (p. 526) that they were variations in the direction of the motion of the ice 

 at different times. For most we must assume that the great ice sheet was 

 affected by the greater irregularities of the bottom over which it flowed, 

 just as — to use the illustration given by Prof. J. D. Dana (to whom we owe 

 this explanation and its application to the anomalous north-south direction 

 of the ice in the Connecticut Valley) — a mass of pitch flowing down an 

 inclined boai'd upon whicli strips had been nailed at vainous angles to 

 the line of inclination would in its under parts be deflected behind the 

 strips and flow in the direction of the grooves thus produced. Ice, in short, 

 though moving with extreme slowness, comports itself like a fluid and 

 obeys the laws of hydraulics. Thus the line of motion for the great 



' C. U. Shepard, Report on Chester Emery Mine, p. 5. 



